the intersection of sets A and B, symbolized by an upside-down U, is the set containing all the elements that are common to both set A AND B. Elements that are shared between both sets.

set A = {1,3,9,12}

set B = {1,2, 4, 6, 8, 9}

the intersection of set A and B are {1,9}

middle part in the venn diagram that gets shaded the union of set A and set B, symbolized by A U B, is the set containing all the elements that are members of set A OR set B ( or of both sets)

set A = {1,2,3,4,5}

set B= { 2, 4, 6, 8}

the union of set A and B are {1,2,3,4,5,6,8} ;