What do you mean by the term difference of sets

The difference of sets A from B, denoted by A - B, is the set defined as A - B = {x | x ∈A ⋀ x ∉ B}

Example 1: If A = {1, 2, 3} and B = {1, 2, 4, 5}, then A - B = {3}.

Example 2: If A = {1, 2, 3} and B = {4, 5}, then A - B = {1, 2, 3}.

Note that in general A - B ≠ B - A