Compiling is the process of converting source code written in a programming language, like Python or Java, into machine code that a computer can execute. This transformation is performed by a program called a compiler, which analyzes the source code for errors and optimizes it for performance. Once the source code is compiled, it produces an executable file that can run on a specific operating system. This allows developers to create software applications that can be distributed and used on various devices, ensuring that the code functions correctly and efficiently on the target hardware.