From what I can tell, "open source" does indeed mean "the source code is freely accessible." From Wikipedia:

> Generally, open source refers to a computer program in which the source code is available to the general public for use and/or modification from its original design. [1]

I think what you are referring to are "OSI Approved Licenses" (OSI = Open Source Initiative, which is an entity). The OSI defines its Open Source Definition which sounds very much like yours. Importantly, the following sentence can be found in the Wikipedia article describing open source licenses:

> One popular set of open-source software licenses are those approved by the Open Source Initiative (OSI) based on their Open Source Definition (OSD). [2]

Sure, "don't use Wikipedia as a reference". But we're dealing with colloquialism here, so I think it's actually pretty accurate. Colloquially, it seems that "open source" != "OSI approved". I have seen people capitalize "Open Source" in an attempt to indicate that they're referring the Open Source Definition, but this is confusing in my opinion, and it really would be more clear to just say "OSI approved".

[1] https://en.wikipedia.org/wiki/Open_source

[2] https://en.wikipedia.org/wiki/Open-source_license#OSI_approv...