That's the FAQ relating to the use of the OSI trademark.
You might be better off linking to the definition of open source, per the OSI, since 2006:
Eitherway, this is why open source zealots tend to specifically say F/LOSS (free / libre open source software), to avoid any ambiguity with people who like to claim 'open source' is ambiguous and easily conflated with 'source available'.
...That there are so many of them proves their own point, I guess!