What does a ! mean in math terms?

This is called a "factorial"......it is the procuct of all the positive integers up to, and including, "n"

For example.....  n!   ....  where n = 3....we have     1 x 2  x 3   = 6

Or  .....   n!  ....    where n = 4 =    1 x 2 x 3 x 4 = 24

This concept is very useful in statistics and probabilty in "counting" operations

BTW  ....   0!   is defined to be =  1

it means you multiply all the numbers up to that number together. for example, 5! = 1*2*3*4*5 or 120

see: http://web2.0calc.com/questions/what-does-the-meaan

Thanks Heureka 

I always forget about that left factorial.  I am really pleased that you reminded me :))