i am vaguely familiar with software licensing is GPL type of open source?

You could say that, LOL. It's the OG of "copyleft" licenses (the guy that made it invented the concept), although "permissive" licenses (BSD, MIT) existed before.

"Copyleft" and "permissive" are the two major categories of Free Software (a.k.a. "open source", although that term has different connotations) license. The difference between them is that "copyleft" requires future modifications by people other than the copyright holders to be released under the same terms, while "permissive" does not. In other words, "copyleft" protects the freedom of future users to control their computer by being able to modify the software on it, while "permissive" maximizes the freedom of other developers to do whatever they want with the code (including using it in proprietary apps, to exploit people).

See also: https://www.gnu.org/philosophy/free-sw.en.html