What does this terminology mean?

[Dustobusto]

So in finding a pattern for the nth derivative for y = x^-1 the book wrote

y⁽ⁿ⁾(x) = (-1)ⁿn!x^-n-1

What does the exclamation mark mean? I know != means not equal to.

 

[milesyoung]

It means factorial:
http://en.wikipedia.org/wiki/Factorial