I joined Caldera in November of 1995, and we certainly used "open source" broadly at that time. We were building software. I can't imagine a world where we did not use the specific phrase "open source software". And we were not alone. The term "Open Source" was used broadly by Linus Torvalds (who at the time was a student...I had dinner with Linus and his then-girlfriend Ute in Germany while he was still a student)