Open source should really NOT be used to describe to anything that isn't copyleft.
The concept of copyleft was literally created because open source wasn't open enough for its creator.
If someone can take the code, modify it, and close it because of a deficient license like BSD or MIT, it's not really open, and never really was.
"Open" meant "documented and interoperable" in UNIXland for many years. Open Source's origins are in the security community's use of the same phrase to mean an intelligence source anyone could get information from. The first programmable computers came from military efforts, and the bulk of computers were military until they became inexpensive, so this relationship was well-established and fundamental, therefore influential.
BSD and MIT are absolutely, positively, 100% Open Source licenses. They (and other code sharing licenses) were referred to as such before Christine Petersen ever claimed to have invented the phrase, which is why the OSI doesn't have the right to define it and also why their lawyers told them that they couldn't copyright it, and also why you're wrong.