(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.