What does! Mean in math?

Answer: n Mathematics ! is the factorial sign.

Let's look at the explanation to understand it better way.

Explanation:

If n is an natural number greater than or equal to 1, then

n! read as (n factorial)  = n × (n-1) × (n-2) × (n-3) × ... × 3 × 2 × 1

example 5! = 5 ×4 ×  3 × 2 × 1 =  120

Thus, In Mathematics ! is the factorial sign.