There are many different definitions of what "Open Source" means. We can have a lovely argument over a pint as to whether GPLv3 is too open or if a licence which hasn't been validated by the OSI counts. But, more fundamentally, I think Open Source roughly falls into seven levels.
The article then briefly describes the 7 levels in non-technical terms as:
- Look but don't touch
- Do What Thou Wilt
- Do As You Would Be Done By
- I'd rather you didn't
- Contributors Welcome
- Blessed Contributors
- The Future
(The "seven levels" link in the quote was a nice surprise.)