What is "euler diagram"

Euler diagram (, - based on standard German pronunciation of "eu") is a diagrammatic means of representing sets and their relationships. The first use of "Eulerian circles" is commonly attributed to Swiss mathematician Leonhard Euler (1707–1783). They are closely related to Venn diagrams. Typically overlapping shapes, usually circles, are used, and an area-proportional or scaled Euler diagram is one in which the area of the shape is proportional to the number of elements it contains.

Venn and Euler diagrams were incorporated as part of instruction in set theory as part of the new math movement in the 1960s. Since then, they have also been adopted by other curriculum fields such as reading.