A set theory symbol representing the empty set containing no elements.
Examples
Basic set theory notation for empty set
A \cap B = \emptyset \text{ means sets A and B are disjoint}
Set builder notation with empty result
\{x \in \mathbb{N} : x^2 < 0\} = \emptyset
Properties of empty set
|\emptyset| = 0 \text{ and } \emptyset \subset A \text{ for all sets } A