What is an exclamation mark?

Algebra Level 3

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

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