system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What does "open source" mean when people are referring to software and programs?
gpt
When a programmer works on an application, the file or files they produce are usually called "source code", and those files are used by a compiler to build an executable program.

"Open source" means that a project team has intentionally posted their source code publicly, so that anyone can inspect it. Other programmers can read the code to see exactly how the program was built and what it does, which allows others to learn from the code, audit it for bugs or security issues, and potentially contribute patches back to the project.

Many open source programs are free to use, and people tend to associate the two ideas, but it's not necessarily a requirement.

You can find many open source projects on websites like GitHub or BitBucket, which provide free hosting for those projects.