intelligence
A term used to describe the potencies such abilities as application of knowledge, amount of logic, creativity (to some extent), memory (to a lesser extent), and general comprehension, among animals. Intelligence is, often, something lacking in most human beings. Intelligence is relative to one person; what you and I, for instance, perceive as stupid may contradict eachother, or vary in degrees.

Today, people often confuse knowledge and determination (especially in academics) with intelligence. Understand; these are NOT the same things. Knowledge is, of course, the amount of information a person mentally contains. Determination is, naturally, the want to go to often extreme measures to achieve your aims or goals. While intelligence is useless without knowledge, the contrary - knowledge without intelligence - is equally useless. 

Much of the time, IQ tests are associated with intelligence. While these are, currently, the most accurate "measurements" of intelligence (if properly executed), they are by no means definitive. They don't consider creativity, abstract logic, or any other trait generally considered intelligent. Still, intelligent people tend to receive higher scores than their mediocre counter-parts. One must also take into account that often times, things like vocabulary are used in such tests. In English, vocabulary, often times, requires definitive knowledge of Latin, German, or French, if not the English language, due to the roots not being absolutely apparent in all cases. 
Man, I possess so much intelligence. I mean, just look at that monsterly definition.