“Open source” means something too. The control people have is in using shared definitions.
Language is malleable, so if enough people use a word incorrectly it changes the definition. But those people get to be called wrong for years until enough people misuse it to make it right.
IMO, MIT & BSD give downstream developers more rights and are indifferent to end-users. GPL gives users more rights, and indifferent to downstream developers.
Is MIT not free because it requires attribution? Is no code free because it cannot be used in ways that break the law?
Just because there are some restrictions does not make it completely unfree, and its fair for people to want to use what is the most natural word to refer to thing that are free enough for them. "OSI-approved" works if you want to be precise but one org does not have the right to dictate the use of a word as common as "open".
I don’t think there’s a true, single definition, but I think maybe the closest to that would be https://en.wikipedia.org/wiki/The_Free_Software_Definition