Assembly language is a low-level programming language that is closely related to machine code, which is the set of instructions executed directly by a computer's CPU. It uses symbolic representations of binary instructions, making it easier for programmers to write and understand than raw machine code. Each assembly language is specific to a particular computer architecture. Programs written in assembly language are translated into machine code by a program called an assembler. While assembly language allows for more control over hardware and can lead to highly optimized code, it is generally more complex and less portable than higher-level programming languages like Python or Java.