An intelligence quotient, or IQ, is a score derived from one of several standardized tests designed to assess intelligence. The abbreviation 'IQ' comes from the German term Intelligenz-Quotient, originally coined by psychologist William Stern. When modern IQ tests are devised, the mean (average) score within an age group is set to 100 and the standard deviation (SD) almost always to 15, although this was not always so historically. Thus, the intention is that approximately 95% of the population scores within two SDs of the mean, i.e. has an IQ between 70 and 130.
Contributions by Quizkajer, Ultramarine, and Drummond.