TrueCrypt IS Open-Source. You can read the source.
Depending on whose definition you accept, simply being able to "read the source" does not make something "open source". While not accepted by everyone, the Open Source Initiative's "Open Source Definition"[1] is a very widely accepted definition of what it means to be "Open Source".
I would posit that "Shared Source"[2] is a more accurate term for a project where the source is available, but the license doesn't permit all of the things required by the OSD.
Yes, there's some confusion because the term "open source" was around before OSI attempted to define it.
If my understanding is correct, the TrueCrypt developers were attempting to make an "OpenSource(tm)" license, but the OSI folks had some technical objections. So the software falls into a gray area where it's not quite officially OpenSource, but it still could be modified and distributed by third parties.
> Yes, there's some confusion because the term "open source" was around before OSI attempted to define it.
No, it was not. OSI coined it. Specifically, Christine Petersen coined it.
It appears to be such a natural term now that we have become convinced that we were using it before OSI, but we weren't. The earliest OED citation for "open source" is from 1998, around the time when OSI coined it. If you have an earlier citation, please submit it to the OED. I don't believe one exists.
There is an unrelated term "open source intelligence" which is indeed older, but nobody called software "open source" before OSI.
I don't know why Bruce Perens apparently trademarked a bunch of things but not "open source" itself. However, as part of its trademark policy, OSI asks that people do not call software "open source" if it's not under an OSI-approved license:
Depending on whose definition you accept, simply being able to "read the source" does not make something "open source". While not accepted by everyone, the Open Source Initiative's "Open Source Definition"[1] is a very widely accepted definition of what it means to be "Open Source".
I would posit that "Shared Source"[2] is a more accurate term for a project where the source is available, but the license doesn't permit all of the things required by the OSD.
[1]: http://opensource.org/osd-annotated
[2]: http://en.wikipedia.org/wiki/Shared_source