Question

What does this symbol mean in math? " ! "

Answer 1

"!" totally means that it is the factorial of the number so for example 2! = 1*2
3! = 1*2*3 

Answer 2

It means FACTORIAL. It is used to mark the multiplicative total of all the previous numbers. just for an example
1!=1
2!= 2×1
3!=3×2×1
4!=4×3×2×1
5!=5×4×3×2×1
and so on..