Complement

Complement is a general term used in many disciplines to denote something that completes a whole. In common use, a complement is something that completes or goes well with something else. In mathematics, the complement of a subset A with respect to a universal set U is the set of elements in U that are not in A; it is denoted A^c. The complement satisfies A ∪ A^c = U and A ∩ A^c = ∅. In probability, the complement of an event A is the event that A does not occur, with P(A^c) = 1 − P(A).

In logic and computer science, the complement refers to negation: the truth-valued opposite of a statement or bit. In Boolean algebra and digital circuits, the NOT operation yields the complement. In computing, the one's complement of a binary word inverts all bits; the two's complement is used to represent signed integers and is obtained by inverting bits and adding one.

In linguistics, a complement is a word or phrase that completes the meaning of a predicate, verb, or adjective, such as "give the man a book" (the object "a book") or "seem tired" (the subject complement "tired").

In immunology, the complement system is a cascade of plasma proteins that enhances the body’s immune responses, including opsonization, inflammation, and lysis of pathogens. It can be activated via classical, lectin, or alternative pathways.

In nutrition, complementary proteins are two or more plant-based or dietary protein sources that, taken together, provide all essential amino acids in adequate amounts.