An assembly routine, also called an assembly language routine, is a set of instructions written in assembly language that performs a specific task, function or operation. There are several synonyms for the term assembly routine, including assembler code, machine language code, low-level language code, and microcode. These terms are often used interchangeably, but they refer to specific types of code used in computer programming and software development. Assembly routines are essential in creating efficient and optimized code for various systems, from embedded systems to operating systems. They require specialized skills and knowledge of computer architecture and hardware, making them vital in the field of computer engineering.