I think another name is called: Binomial Coefficient. Like 4 choose 3 = 4! / (3!*(4-3)!)
When would this be used in the real world, if that make sense.
The number of ways that 5 children can be chosen from 8 is 8 chose 5 or 8C5
So it is used in counting problems.
Also note that every time 5 children are chosen, 3 are not chosen.
Or more generally
nCr = nC(n-r)
If that is not quite what you want to know then say so and someone, maybe me, will try to help further. :)