In computer programming, source code is (generally speaking) a text file version of a computer program or software that contains instructions that the computer follows to do something. Source code is written in a programming language which a human can read and change. A large program may contain many different source code files that all work together. Source code is in many cases compiled before running it. That means translating the code into assembly language or machine language which is much faster and easier for the computer to read, but hard for a human to read. Another very common way is to interpret the code, without needing a compilation step, while that's generally slower.