New listing UCLA BRUINS ADIDAS 1/4 ZIP POLO SHIRT (LRG) NW/TAGS SKY BLUE W/SEWN LOGOS.
It compares people of the same age or age category and assumes that IQ is normally distributed, that the average (mean) is 100 and that the standard deviation is something like 15 (IQ tests sometimes differ in their standard deviations).
There have been multiple classifications or tests for IQ, but the common conclusion places the normal or average IQ at 90 to 110. Tests for IQ are sometimes subjective based on the testing criteria and application, but the science is constantly evolving as new information about intelligence is uncovered.