The Venn diagram also called as the set diagram is used to depict set operations. It was discovered by John Venn and hence named after him. It was also used by Leonard Euler, the great Swiss Mathematician. So, these are sometimes called as the Venn - Euler Diagram or simply the Venn diagram.
These diagrams show the logical relationship among the sets under consideration. These relationships include all three basic operations - Intersection, Union, Complement. The Venn Diagram makes the entire concept very clear. Venn diagrams are also used in other fields like Statistics, Computer Science etc.