L1

From Language 1 (“first language”).

L1 (plural L1s)

1. A mother tongue; someone's native language; own language.

   Coordinate term: L2

   • 2017, Di Zou, James Lambert, “Feedback methods for student voice in the digital age”, in British Journal of Educational Technology, volume 48, number 5, page 1085:

     This advantage was pertinent in the Hong Kong context where English is largely an L2 language, although would not be expected to be as large in an L1 context.

L1

1. (astrophysics) Abbreviation of Lagrange point 1, located between the larger and smaller objects along a line connecting the two.

• (astrophysics): Lagrange point, L2, L3, L4, L5

From Level 1.

L1 (uncountable)

1. (computing) Short for first level in various contexts.
   1. (computing) The first-level cache of a processor, closer to the processor than the second-level cache.
      • 2009, Sandeep Koranne, Practical Computing on the Cell Broadband Engine‎, →ISBN, page 22:

        Writing of the L1 is performed one cache line at a time and can be 64 bytes or 32 bytes.

   2. (networking) The physical layer in the seven-layer OSI network model.

The first level cache is more often written as L1 cache than as L1 except when used attributively in writing meant for a technical audience.

• 1L