An assembler is a type of computer program that translates assembly language, a low-level programming language, into machine code, which is the binary code that a computer's processor can execute. Assembly language uses mnemonics and symbols to represent machine-level instructions, making it easier for programmers to write and understand code compared to raw binary. Assemblers play a crucial role in software development, especially in systems programming and embedded systems, where performance and hardware control are essential. By converting assembly language into machine code, assemblers enable developers to create efficient programs that can directly interact with the computer's hardware, such as CPUs and memory.