What is an exclamation mark?

Algebra

$\prod_{m=4}^{4^2} \dfrac{\big(m^2-1^2\big)\big(m^2-2^2\big)}{m^2\big(m^2-3^2\big)}$

If the value of the product above is equal to $\frac AB$ , where $A$ and $B$ are coprime positive integers, find $A-B$ .