1. of a set, S, with respect to some universal set U. The set consisting of elements that are in U but not in S; it is usually denoted by S′, ~S, or S̶. Formally,
The process of taking complements is one of the basic operations that can be performed on sets.
The set difference (or relative complement) of two sets S and T is the set of elements that are in S but not in T; it is usually written as S—T. Thus
See also operations on sets.
3. of a subgraph G′, with vertices V′ and edges E′, of a graph G, with vertices V and edges E. The subgraph consisting of the vertices V and the edges in E but not in E′.
4. See radix-minus-one complement. See also complement number system, radix complement.