Here's some paraphrased history on IQ for you:
Intelligence Quotient (IQ) tests were initially designed by psychologists Alfred Binet and Theodore Simon (The Binet-Simon scale) to distinguish children who might need special education (later revised by Stanford University becoming the Stanford-Binet scale). The idea of the IQ test is to compare your own mental age against a standardized 'norm' and covers a wide range of abilities such as imagery, attention, comprehension, imagination, and memory.
There are thought to be multiple kinds of 'intelligence' such as verbal, musical, logical/mathematical, spatial, bodily (such as dancing/athletic skills), and personal/emotional (self-awareness and awareness of others in terms of feelings).
IQ scores show high correlation with academic success so it is thought to be both a reliable and valid method.