In most intelligence measurement systems, an intelligence quotient of over 130 is considered very superior; 120 to 130 is superior; from 110 to 120 is high average; and from 90 to 110 is average. About half of all people fall in the "average" category, according to the journal Science.
Originally, IQ was measured as a percentage comparison between one's chronological age versus one's intellectual age. More recently, researchers have calibrated tests so that they are a population comparison, with an intelligence of 100 being exactly average. There is great debate among cognitive scientists as to what an IQ test really measures, though, with problems from cultural bias to the motivation of the test taker being identified as reasons for low scores.