> linux is completely described by its source code.
I would say that linux is defined by the way its source code [in C] runs on machines [of various kinds]. It's also helpful to know some history, especially of unix, for context. And the communities of people that use linux. I think there's more to understanding linux, or even describing it, than the source code only.
Both statements depend on your ability to devote time and appropriate expertise to discerning the documentation.