- The OSI claims to have coined the term in 1988 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...
On a separate note the OSI's original mission statement was (https://web.archive.org/web/20000408035603/http://opensource...)
> The Open Source Initiative's mission will be to own and defend the Open Source trademark, to manage the www.opensource.org resources, to develop branding programs attractive to software customers and producers, and to advance the cause of open-source software and serve the hacker community in other appropriate way
Which they since abandoned because "there is virtually no chance that the U.S. Patent and Trademark Office would register the mark "open source"; the mark is too descriptive" (and one suspects because the mark was already in use in trade of software, see the xent.com link above) https://opensource.org/pressreleases/certified-open-source.p...
They have no special rights to the term open source. I wish people (including the OSI) would stop pretending otherwise. You can think that it's a good idea to use their definition without relying on falsehoods.