The Free On-line Dictionary of Computing (30 December 2018):

assembly language
ASM
assembly code

    (Or "assembly code") A symbolic representation of
   the machine language of a specific processor.  Assembly
   language is converted to machine code by an assembler.
   Usually, each line of assembly code produces one machine
   instruction, though the use of macros is common.

   Programming in assembly language is slow and error-prone but
   is the only way to squeeze every last bit of performance out
   of the hardware.

   Filename extension: .s (Unix), .asm (CP/M and others).

   See also second generation language.

   (1996-09-17)