Intelligence quotient (IQ) is a measurement of how well people learn or solve problems and, according to most tests, a high IQ would be anything above about 110. Most experts consider anything above 120 to be very high, and most consider anything above 140 to be in the genius range. IQs between 90 and 110 are usually considered average under most metrics. There are many different kinds of tests used to measure IQ, and they may yield slightly different results with different people because they focus more heavily on different aspects of the thinking process.
According to experts, many people have the wrong idea about what IQ really represents. For example, some people think that anybody who knows many facts and is extremely knowledgeable would have a high IQ. Sometimes this can be true, but not always. IQ simply measures a person's ability to solve problems, deal with new situations, and learn things quickly. Some people become experts in their fields with only an average ability in these areas by applying themselves more thoroughly, and some people with very high IQs never really use them for anything that greatly benefits their lives.
IQ tests often challenge people in very different ways, and this can make them produce different results. For example, some tests are timed while others aren't, and someone who scores very high on a test without a time limit might do somewhat worse on the timed test. There are also IQ tests with slightly different focuses; some may focus more on abstract thinking, for example, while others may test mathematical calculation abilities more rigorously. Someone who has a learning disability with math might do very well on every other aspect of an IQ test, and will generally measure much higher on tests with less of a math focus.
Studies have suggested that a person's IQ can be a pretty good predictor for success in life, but it is not generally considered the best indicator. Some tests have been developed that measure a person's aptitude for self-discipline, and these have generally shown this trait may be much more important. Most of the studies on this have been performed on school children, so there is some uncertainty about how well it translates to adult life. There is also some question about whether or not IQ tests fully measure all the important thinking abilities, and some think they fail to capture many important factors of intelligence, such as imagination.