A Venn diagram uses overlapping circles or shapes to show logical relationships between sets.
Venn diagrams visually represent set operations: union (all elements in either or both circles), intersection (overlapping region), complement (outside a circle), and difference. They are used in probability, logic, statistics, and computer science (database queries). Two-circle Venn diagrams show relationships between two sets, while three-circle diagrams (eight regions) are common for three sets.
Venn diagrams were introduced by John Venn in his 1880 paper "On the Diagrammatic and Mechanical Representation of Propositions and Reasonings." Similar diagrams were used earlier by Leonhard Euler (Euler diagrams) in the 18th century. Venn's innovation was making the diagrams more general and inclusive.