What "count backs" means to me is this: a method of learning subtraction by counting backwards from the first number in the problem to get to the answer.  For example, 11 minus 3 would be

11 take away 1 is 10
10 take away 1 is 9
9 take away 1 is 8

It's the verbal equivalent of "counting on your fingers" for arithmetic.

Count-backs aren't meant to be a long-term technique for doing subtraction.  They are meant only to teach the concept of subtraction - what it means to subtract one number from another.

Here's a simple worksheet for practicing count-backs on fairly small numbers:

http://tinyurl.com/countbacks-worksheet