"Open" is a pretty vague word which could mean all sorts of things.
"Open source" is defined by the Open Source definition according to the OSI [1]. In saying that, I realize that every couple of years somebody tries to claim that their understanding of the term "open source" should trump the one the community has settled on. I personally am not ready to acquiesce to this semantic drift, at least, not yet.
[1] - https://opensource.org/osd/
