I've always defined intelligence as someone's ability to apply their knowledge in unfamiliar contexts. An intelligent person can think quickly and logically, relate ideas to situations, communicate effectively, recognize patterns, and minimize the amount of work required to overcome obstacles. Knowledge is simply a tool for the intelligent.
Many people seem to think these two terms are synonyms, which is why so many doctors and engineers are unqualified: Knowledge was stressed for their entire education instead of intelligence and problem solving. This analogy also works for SC, and really for any context in life. You'll see people cramming up frames and combos, but in the end they're just scrubs that know a lot about the game because they are not intelligent (or simply don't use their intelligence).