The IQ test was invented by Alfred Binet as a way of identifying people who were having trouble in school because they were mentally slow. For this he came up with a large number of different questions that exercised the brain in various ways, and figured out how well an average kid would do. When he gave the test to a real kid he would take their performance and figure out a "mental age" that they performed at. Their intelligence quotient was then defined as 100 * (mental age) / (physical age).
The development of IQ tests aimed at adults which are defined based on a bell curve was a later innovation. The name was kept simply because it was then well-known.
The value is defined by your test results. The tests generate scores that are roughly normally distributed up to about an IQ of 130 (two standard deviations), but then have many more people at high IQs than a bell curve would predict.
Most IQ tests can't even measure above 155 or so, anyway, and they obviously can't measure below 0. So it's a little silly to talk about them being normally distributed.
The IQ test was invented by Alfred Binet as a way of identifying people who were having trouble in school because they were mentally slow. For this he came up with a large number of different questions that exercised the brain in various ways, and figured out how well an average kid would do. When he gave the test to a real kid he would take their performance and figure out a "mental age" that they performed at. Their intelligence quotient was then defined as 100 * (mental age) / (physical age).
The development of IQ tests aimed at adults which are defined based on a bell curve was a later innovation. The name was kept simply because it was then well-known.