Elements - The members of a set.
Intersection - The intersection of two sets, denoted A∩B ("A intersect B") is the set of all members contained in both A and B.
Union - The union of two sets, denoted A∪B ("A union B"), is the set of all members contained in either A or B or both.
Venn diagram - A representation of two or more sets that shows the relationship between them:
Venn Diagram