A Venn diagram is a diagram that shows all possible logical relations between a finite collection of sets. The three circles represent the three sets: A, B, and C. The area where all three circles overlap is the set of elements common to all three sets (elements in both A and B or in both B and C or in both A and C). The area where only two circles overlap is the set of elements common to only two sets (elements in either A or B but not both, or elements in either B or C but not both). And finally, the area where no two circles overlap is the set of elements that are unique to one set (elements found only in A but not found either in B or C).