Source code (sometimes just “source” or “code”) is human-readable computer instructions written by programmers. It’s the original form of a computer program before it gets converted into a format that computers can execute directly.

Here’s an example of some source code written in the Python programming language:

def do_twice(func):
    def wrapper_do_twice(*args, **kwargs):
        func(*args, **kwargs)
        func(*args, **kwargs)
    return wrapper_do_twice

@do_twice
def greet(name):
    print(f"Hello, {name}!")

When programmers talk about “reading the source” or “checking the source code,” they mean examining these original, human-readable program files. The source code represents the authoritative version of how a program works and contains all the implementation details of its functionality.