A binary operator representing set difference or relative complement in set theory and logic.
Examples
Set difference notation
A \setminus B = \{x \in A : x \notin B\}
Concrete set difference example
\{1,2,3,4\} \setminus \{2,4\} = \{1,3\}
Number set difference
\mathbb{R} \setminus \mathbb{Q} = \text{the irrational numbers}