In mathematics, a set is a well-defined collection of distinct objects, considered as an object in its own right. For example, the numbers 2, 4, and 6 are distinct objects when considered separately, but when they are considered collectively, they form a single set of size three, written {2,4,6}.
Sets are represented in a Venn diagram by circles drawn inside a rectangle representing the universal set. The region outside the circle represents the complement of the set. The overlapping region of two circles represents the intersection of the two sets. Two circles together represent the union of the two sets. A Venn diagram is an illustration of the relationships between and among sets, groups of objects that share something in common. The drawing is an example of a Venn diagram that shows the relationship among three overlapping sets X, Y, and Z. A Venn diagram is an illustration that uses circles to show the relationships among things or finite groups of things. Circles that overlap have a commonality while circles that do not overlap do not share those traits. Venn diagrams help to represent the similarities and differences between the two concepts visually. Venn diagrams were invented by a guy named John Venn as a way of picturing relationships between different groups of things. Since the mathematical term for "a group of things" is "a set", Venn diagrams can be used to illustrate set relationships.