Wiktionary and Wikipedia are sister projects; both are wikis and have a similar appearance. The way we do things here is similar in some respects to the way things are done at Wikipedia, but in other respects it's very different. As a general rule, Wiktionary is not Wikipedia; some of our policies are similar to some of Wikipedia's policies, others are quite different. None of the policies of Wikipedia apply here, but of course Wiktionary does sometimes have policies that are similar to their Wikipedia counterparts (such as WT:AGF). This page is meant as a guide to those who have some experience editing on the English Wikipedia, but little or none on the English Wiktionary.
Wiktionary has several policies and guidelines regarding what can be included, as does Wikipedia. Neither Wiktionary nor Wikipedia are intended for any kind of information to be added indiscriminately. Both projects require some form of verification that the information being presented is accurate, and neither project is for "things made up one day". However, being a dictionary and not an encyclopedia, Wiktionary of course has some different rules regarding the inclusion of terms, which differ in important ways from the policies at Wikipedia. The most important policy on Wiktionary is our criteria for inclusion (CFI). This is our "holy scripture", and it is the primary means by which we judge content on Wiktionary. It is analogous to Wikipedia's policies on verifiability and notability.
Wiktionary is more objective than Wikipedia about what it includes. Our goal is to describe every language, the way it is used or has been used, from a neutral point of view. That means that if something is a word and can be demonstrated to be in use (on which see below), then it can be included. Being descriptive from a neutral point of view means we have no "notability" requirement, as there is no objective criterion for the notability of a word. It means that we consider the speech varieties of all users of a language equally valid: we consider the English of the British King just as valid as that of a farmer in the Australian outback. We do not judge whether usage is correct or incorrect, we only document whatever usage exists or has ever existed among speakers (or writers). Consequently Wiktionary allows any attested terms, no matter how rare or obscure, and no matter how strangely spelled, no matter how unusual the grammar. We also document the attitudes that speakers/writers themselves have towards certain usage, if necessary. So if something is commonly considered bad usage, we still include it, but we also include a notice saying that it's commonly considered bad usage. If it is rarely used, archaic or no longer understood, we also include it with a notice saying so. As long as it meets the criteria for inclusion, it can be added.
Many languages, including English, use different inflected forms of words. These are treated on Wiktionary as words in their own right, and are given separate entries with definitions. This is different from Wikipedia, where pages are about concepts. Wikipedia article names are usually nouns, and different forms or spellings are generally regarded as referring to the same thing, so a redirect is created. But as we deal with words, and hands is a different word from hand, and closed is distinct from close, we treat them as distinct and give each their own entry. This implies that there are very few redirects; most of the cases where a redirect would be warranted on Wikipedia, a separate entry is created on Wiktionary.
This doesn't mean we repeat the same information on each of those entries, though. One form of a word, often the most basic form, is treated as the lemma form. The lemma entry is treated as kind of a stand-in for all possible forms of the word, in the same way that a Wikipedia article might have one "proper" title and have other possible forms of the name as redirects. But as mentioned, on Wiktionary we generally do not create redirects for such forms, but give them their own entry with a minimal definition that includes a link to the lemma form. Such entries are referred to as "form-of entries" (because their definitions usually include "form of") or "non-lemmas" on Wiktionary. They are often very simple, consisting only of a heading and a form-of template, which links back to the main term. Because form-of entries are often so simple, many of them are created automatically using various bots.
There is a practical reason for this approach to redirects. A word can be both a lemma and an inflected form of another lemma. While saw is the past tense of see in English, it is also a noun. Additionally, Wiktionary includes terms in all languages, not just English, so it's possible what is a lemma in one language is an inflected form of another lemma in another language. For example, golden is a lemma in English, while it is a past-tense form of the lemma gelden in Dutch. A consequence of this treatment of words, forms and lemmas is that there are no "disambiguation pages" on Wiktionary; each entry may contain definitions for several distinct words that are spelled the same way (homographs), but have different meanings in the same or different languages.
Wiktionary's page names are case sensitive, unlike Wikipedia's. On Wikipedia, all article names implicitly begin with an uppercase letter, even if you type a lowercase letter in the title or link. However, this does not work on Wiktionary. Hand and hand are different pages and are not interchangeable. This is sometimes a source of confusion for new users, but tends to come as second nature to more experienced editors. When several pages exist that differ only in their capitalisation, the template {{also}} is placed at the very beginning of the page to link between them, so that users can easily navigate between different capitalisations of the same word. The template is also used to link to other terms that use letters with diacritics or are otherwise similar in appearance to the current term, to help users who are unsure about the diacritics used (if the language is foreign to them) or if they don't have the right keyboard to enter them with.
Wiktionary has a rather different way of providing references for its information. References on Wikipedia are generally sources that corroborate a certain piece of information; they basically say the same thing that Wikipedia says. This is because Wikipedia is a tertiary source, and does not do any researching on topics. It only documents what others have already discovered and documented about a topic; Wikipedia does not allow original research. However, for a word to be verified as being attested, we require proof that it is in use or has been in use, and that the definition given is the one that its users intend. This makes the style in which Wikipedia provides references inadequate. After all, there are many sources that say "X is a word that means Y" out there in the world, in particular other dictionaries. But they don't actually prove that people use a word, they just say they do, which really isn't sufficient. There have been several times when dictionaries have made up words that nobody has ever used!
Wiktionary is a secondary source. Rather than trying to document the words that others have documented, we do all the documenting first hand. This means that to prove a word exists and is in use, we need to cite actual usage, not documentation of that usage. We research and cite usage that happens "in the wild" so to say, rather than relying on what other sources say about something. And as a consequence, we don't have any policy on original research; sometimes original research is inevitable and necessary to help us document a rare or brand-new use that no one else has documented before. Importantly, Wiktionary allows attestation from any durably archived source, which includes not just "credible" or "reliable" sources. As our aim is to be descriptive and neutral, we don't discriminate between different speakers of a language, as noted in the section above. This means that we allow citations from colloquial sources such as Usenet, if they are considered durably archived for Wiktionary's purposes.
This doesn't mean that definitions themselves can't be taken from dictionaries (as long as it's not a copyright violation of course), nor does it mean that we can't include links to other dictionaries or reference works. However, it does mean that such works don't constitute proof of usage, so they can't prevent an entry from being deleted due to lack of sources. Instead, it is better to treat them as a service to our users, who may want to know more about a word, or want to be able to compare definitions to see if we're not missing something important.
Citations are normally added to the entry itself or to the entry's citations page. The link and URL for the citations page contains "Citations:" as a prefix to the entry's name (just as "Talk:" is the prefix for the talk/discussion page). Most words on Wiktionary, however, don't have any citations. This is mostly for practical reasons. Many words are obviously in use and nobody would try to question that; it would just be a waste of time that's better spent on improving other parts of the dictionary. Nevertheless, the burden of proof is on the citations, and if someone is not convinced that a word exists without some proof, they can call for it to be verified. A user can submit a word for verification by placing the {{rfv}} or {{rfv-sense}} template on the entry, which are similar to Wikipedia's "citation needed" template. The user then creates a new section on Wiktionary:Requests for verification, perhaps with an added note about the nature of the request. At that point, the goal is to find citations for the term that verify its usage, and also the correctness of the definition(s) in the entry. In most cases, this comes down to finding and citing (if the language is prominent) three or more independent uses of the term as mandated by the CFI. If the term cannot be verified after some time, it is deleted, but its citations page is kept for future reference. If new attestations are found later, and added to the citations page, then the entry can be re-created once the required minimum of "good" citations is met.
Wiktionary does not include just terms and their definitions, but also other information about terms such as pronunciation and etymology. Verification of this information (using the {{rfv-pron}} and {{rfv-etym}} templates) follows a similar process, but in this case secondary sources are laudable but not required as references like on Wikipedia as the language material itself allows conclusions by recognized rules of the language sciences, superseding existent or replacing non-existent references; in the case of pronunciations, audio records prove them, in the case of etymologies, likelihoods may be stated according to the collected knowledge and there is no rule like WP:Synthesis – see the entry կաղամախի (kałamaxi) where Wiktionary’s methods, detached from those of Wikipedia, are pushed to the extremes. However, this kind of information is not the mainstay of Wiktionary's content, so it's not submitted for verification as often as terms and definitions themselves are.
As Wiktionary is a dictionary, its pages are often short and simple, and attempt to give a concise but complete overview of everything that is known to Wiktionary about a term. There is very little prose on Wiktionary's entries, and there is little room for variation and creativity with words. The formatting of pages is standardised and documented on Wiktionary:Entry layout (EL), which is Wiktionary's most important policy when it comes to formatting and layout. While it does allow for some variation and differences, it is still a fairly rigid format that all entries are expected to follow.
Because the formatting of pages is so uniform, Wiktionary uses a lot of templates to help create certain parts of entries. Aside from general templates such as {{head}}, {{der}}, {{lb}}, {{l}} and {{m}}, there are many templates that are used only for a single language. Such language-specific templates are used to automatically generate and display inflected forms of terms, and to add entries to the appropriate categories. It's rare to add a category directly to the bottom of a page, usually the templates add them instead. It's a very important part of Wiktionary proficiency to learn to use the proper templates. In fact, it's standard practice to convert raw wikitext to a template if one is available, and remove an explicitly-added category if a template on that page already includes it.
Wiktionary also makes extensive use of language codes. These are two- and three-letter codes that represent a particular language or group of languages, and are defined through Module:languages. For example, "en" refers to the English language, while "cmn" refers to Mandarin Chinese. The language codes are (mostly) standardised, as are the names of the languages they represent; i.e. Mandarin is always written "Mandarin" because Module:languages lists this as the first (primary) name, never "Mandarin Chinese" or any other variation. Knowing the code of the language you are working on is very important, and necessary for almost any kind of editing on Wiktionary. Templates that are specific to a language always have names that begin with the language code, such as {{en-noun}} to generate a headword line for an English noun, or {{es-conj}} to generate a table of conjugated forms for a Spanish verb ending in -ar. Generic templates that are used for all languages often require a language code as a template parameter.
Wiktionary uses categories to organise and group entries and other information, just like Wikipedia does. But because many languages need the same categories, the category structure is standardised (although not by formal policy) and the categorisation is regulated through the use of categorisation templates, which automatically add categories to their parent categories.
Every language on Wiktionary has a single main category, which itself is located in Category:All languages. The main category for English is Category:English language, the category for Russian is Category:Russian language and so on. Within that category, everything belonging to that language is organised. The most important subcategory is the lemmas category, which holds all lemmas in that language by their part of speech (nouns, adjectives, verbs and so on). There are also other categories, such as those organising terms by their etymology, by their lexical properties, or by their dialect.
Wikipedia normally organises articles by topic. While this is not usually possible for many words in a dictionary, Wiktionary does have a tree of topical categories, located at Category:All topics. Every language has its own topical category tree, and the category is added directly to the page. The names of topical categories are slightly different for historical reasons, and begin with a language code rather than a language name. There has been some discussion on changing this, but there is no consensus on what to change it into.
Like Wikipedia, Wiktionary is not just a project but is home to a large and active community of editors. Wiktionary has its own unwritten rules and manuals of style in addition to those discussed above and in other policy pages.
The main discussion room is the Beer Parlour. It is similar to Wikipedia's village pump, and is used for general discussion about many kinds of issues and policies. Next to that is the Information Desk, which is used less to discuss and more to ask questions. The Tea Room is used to discuss terms and anything related to them (aside from verification). The Grease Pit is a technical discussion forum. It is used mainly to discuss templates and modules, since they are so prevalent on Wiktionary. Because there are so many pages on Wiktionary with relatively little content, most editors don't add entries to their watch lists. Talk pages of individual pages are not often used, and discussions added to them tend to get little attention. Instead, discussion about specific entries is usually centralised in the Tea Room, which functions somewhat like a common talk page for all entries.
Wikipedia often encourages users to be creative, and has many pages with humorous themes (including a BJAODN). It also offers a wide array of userboxes that users can add to their personal pages. Wiktionary is more spartan in that respect, and allows only userboxes that are relevant to your work on Wiktionary itself. The most important of these are language userboxes. They are the same as on Wikipedia, and are used on your user page to display the languages and scripts that you know and how proficient you are in them. Because Wiktionary deals with languages so much, these are more important than they are on Wikipedia, so you're strongly encouraged to add them to your user page!
Wiktionary has a different blocking policy than Wikipedia, and is generally less lenient. While we assume good faith on Wiktionary too, we also combat vandalism and other disruptive editing more severely. Warnings are not usually issued unless edits can reasonably be assumed to have been made in good faith. A tenet on Wiktionary is: if someone complains, stop what you're doing and talk first. In good-faith situations, a short block of a few hours to a day or two is often issued to prevent further damage and to encourage discussion if other measures fail.