A compiler is a specialized program that translates code written in a high-level programming language, like Python or Java, into machine code that a computer's processor can understand. This process allows developers to write code in a more human-readable format while ensuring that the computer can execute the instructions efficiently. Compilers perform several tasks, including lexical analysis, syntax analysis, and code optimization. They check for errors in the code and convert it into an executable file, which can be run on a computer. This makes compilers essential tools in software development, enabling the creation of applications and systems.