[aston09]

What is the meaning of the ' symbol in stats. E.g A'

[galactus]

Do you mean what is A'?

That means the complement of A.

The things which are NOT in A.

For instance, suppose we have two sets A and B.

A={1,2,3,4}
B={2,3,4,5}

What is NOT in A? 5.

Therefore, A'={5}