It was in use, both in software and in the world at large (especially the intelligence community). I suppose how it depends how you define "common" but "people use the term in official announcements and assume everyone knows what they mean" seems common enough to me.

- The OSI claims to have coined the term in 1998 https://opensource.com/article/18/2/coining-term-open-source...

- Here is a use of the term, 7 times, and as the main object, from 1996 http://www.xent.com/FoRK-archive/fall96/0269.html

- Here is a use of the term, as a proper noun, from 1993 https://groups.google.com/forum/#!msg/comp.os.ms-windows.pro...

OK, now find me regular usage of "open source", applied to software, by more than one person trying to sell something, as meaning something different from the OSI definition between approx 2000 and 2017.

Why? That's not relevant to your claim that

> "open source" was not in common use at the time that OSI decided to use it.

But I suspect that if you search reddit/hn discussions in that period thoroughly you'll find a few cases... feel free if you want to waste your time.

You haven't shown that "open source" was in common use at the time OSI decided to use it (1988 is earlier than 1996), nor that it's been in common use as meaning something else when applied to software since then. One company trying to sell something doesn't make it common use, either - otherwise I could claim that my water is from a "free source" and declare that for all eternity referring to free source must mean it comes from my specific river.

> (1988 is earlier than 1996)

Oops, that was a typo on my part, the OSI claims to have invented it in 1998 not 1988, updated my original post here too

See the source: https://opensource.com/article/18/2/coining-term-open-source...

Ah, thank you. Either way, one company using the term once before that doesn't mean that it is a phrase in common usage. It also doesn't mean that the term hasn't changed to mean something else in the eyes of hundreds of thousands of developers since them, and using it to mean its plain meaning will only ever cause confusion, and potentially result in people doing things you didn't want with the source code.

Epic, Microsoft, IBM, and hundreds of other companies, big and small, have been careful to avoid this issue specifically because there is an existing definition and it causes confusion.