subset

1. (set theory, of a set S) A set A such that every element of A is also an element of S.Examples: "The set of integers is a subset of the set of real numbers."; "The set #92;lbracea,b#92;rbrace is a both a subset and a proper subset of #92;lbracea,b,c#92;rbrace while the set #92;lbracea,b,c#92;rbrace is a subset of #92;lbracea,b,c#92;rbrace but not a proper subset of #92;lbracea,b,c#92;rbrace."; "1963, David B. MacNeil, Modern Mathematics for the Practical Man, David Van Nostrand, Republished as 2013, David B. MacNeil, Fundamentals of Modern Mathematics: A Practical Review, Dover, page 3, In the foregoing example, the set D of the first four letters of the alphabet, was a subset of the set A of all the letters of the alphabet, because A includes all the members of D."