I enjoyed reading this post: https://words.steveklabnik.com/the-culture-war-at-the-heart-of-open-source
Here is my highlight:
If you ask a random developer what “open source” means to them, you won’t often hear “software that follows the Open Source Definition.” If you ask them “what’s the difference between free software and open source software,” you’ll often hear “aren’t those the same thing?” or “you can charge money for open source software, it’s not always free.” You may even hear “it’s on GitHub.”
In brief, there was a man Richard Stallman (and his team) starting a project called "GNU Project" in 1983. This project was about to develop a free software system. The term "free" here meant "freedom", not only about the price. The Free Software Foundation appeared to support this project. But then, the term "free software" was so ambiguous. "In addition, the ambiguity of the term “free software” was seen as discouraging business adoption.". Then, the Open Source Initiative was founded to support the promotion of the term "open source". "The idea here is plain: Free Software, but for business."
Note:
The sentences in "double quotes with italic style" are cited from the original post.