In my opinion, the term "open source" means "the source [code] is open for people to see". You might be able to stretch that to include "and modify" but that is stretching it.

That is all "open source" really means. It's open for people to see/view. Beyond that, is where a license comes in to restrict or give freedom beyond the term of "open source". That is what OSI does. Adds additional requirements within a license. It cannot change the definition of the term "open source" however.