If you're just looking for a cursory introduction to the underlying concepts, I agree with the other comments that K&R is what you are looking for. I'd add the caveat that due to the fact that C is a tiny language with a tiny standard library, most code you'll see in the wild uses custom concepts/libraries/object models on top of C. So for most practical purposes, there isn't really "C" as much as there is "unix programming C", or "embedded C", or whatever else have you, and all of them add a thick layer on top of the core language.
But for the most part, yes it is about "foundational concepts". A lot of the time when you learn system level programming people will refer to certain quirks or terms from the C world.