IQ test, which stands for "Intelligence Quotient," is a standard score that tells you how much smarter or less smart than your peers are. The average score for this group is 100. By giving the same test to a huge group of people from all walks of life and then getting the average, the IQ number is found. 

For the first time, in 1912, psychologist William Stern used the formula "mental age to chronological age x 100" to show IQ. Let's say someone was 10 years old and thought like a 10-year-old, their IQ would be 100. But if, say, they were 13 years old instead of 10, their IQ would be 130.