*factorial*

n. (Math.) (a) pl. 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. Brande & C.

(b) The product of the consecutive whole numbers from unity up to any given number; thus, 5 factorial is the product of 5 times four times three times two times one, or 120. [ 1913 Webster +PJC ]