Venn diagram 
(vĕn)
(vĕn)n.
A diagram using circles to represent sets, with the position and overlap of the circles indicating the relationships between the sets.
[After John Venn (1834-1923), British logician.]
Venn diagramtop: Sets A and B intersect to form set C.
bottom: Set B is a subset of set A. All members of B are also members of A.