Real Dictionary

factorial in American English
of a factor
the product of a given series of consecutive whole numbers beginning with 1 and ending with the specified number
noun: the product of a given positive integer multiplied by all lesser positive integers: The quantity four factorial (4!) = 4 ⋅ 3 ⋅ 2 ⋅ 1 = 24

factorial in British English
adjective: of or involving factorials or factors
noun: the product of all the positive integers from one up to and including a given integer. Factorial zero is assigned the value of one: factorial four is 1 × 2 × 3 × 4. Symbol: n!, where n is the given integer