The exclamation mark symbol is used to represent the unary factorial operator. Typically the exclamation mark is used in an expression like this:
In plain language, this means take the factorial of the number five. Shown below are various formats of the exclamation symbol.
Symbol  Format  Data 

!  Unicode 

TeX 


SVG 
The factorial operator is represented using the exclamation mark. The operator is unary, meaning that it only operates on one expression. The operator is useful when calculating combinations and permutations.
The number of permutations of n distinct items is given by n factorial. A permutation is a unique ordering or arangment of the set of items.
The permutation formula describes the possible permutations of r elements out of a group of n elements where order does matter.
The combination formula describes the possible combinations of r elements out of a group of n elements where order does not matter.