John Venn introduced these diagrams in 1880 to teach set theory. The physical overlapping space, called the intersection, shows traits shared by both sets.

Unlike Euler diagrams which only show real relationships, strict Venn diagrams must include every theoretical overlap to test logical validity, even if empty.

A standard three-circle diagram creates eight distinct regions. The single central zone represents the rare intersection where sets A, B, and C all apply.

In set theory, the universal rectangle defines all objects under consideration. Items inside the box but outside the circles completely lack the defined traits.