Factorial

[Mark Zuckerberg]

A name given to the factors of a continued product when
the former are derivable from one and the same function F(x) by
successively imparting a constant increment or decrement h to the
independent variable. Thus the product F(x).F(x h).F(x 2h) . . .
F[x (n-1)h] is called a factorial term, and its several factors take
the name of factorials.

[Gregory]

Originally a mathematical term. Denoted as 4! and read as four factorial, its the product of 1x2x3x4=24.
Heard used when describing someone whose clothes are about 10 sizes too tight: Yo, she aint no size four, shes a size four factorial!
Originating in the Manayunk area of Philadelphia, PA, as well as the Philadelphia suburb of Phoenixville, PA, as a word to describe anything or any situation as totally outrageous or ridiculous, it is quickly becoming adopted as colloquialism all over the Philadelphia metro area.

[Lanell]

A tutorial about facts

[Zipporah Schumaker]

The product of an integer and all the integers below it; e.g. factorial four (4!) is equal to 24.