To some people’s surprise, even open-source software has a license attached to it. And with that license comes a description and agreement for what can and can’t be done with the source code of any particular product or service. What exact license the specific open-source software lies under is generally up to the developer(s) and/or current maintainers of the original code.
Open-source software licensing is not something that I have really taken particular notice of in previous and recent times. In fact, all code I have ever created or modified has been done so with no regard to what the license is. I am guilty, yes, as are probably a lot of open-source developers and programmers.