Domain

Domain is a term used across disciplines to denote a defined set of inputs, values, or a geographic or subject area.

In mathematics, the domain of a function is the set of input values for which the function is defined. The codomain is a separate concept that specifies the possible outputs. For example, f(x) = sqrt(x) has domain x ≥ 0. In complex analysis, a domain is a nonempty open connected subset of the complex plane. In abstract algebra, an integral domain is a ring with no zero divisors, enabling cancellation: if ab = ac and a ≠ 0, then b = c.

In computing and networks, domain most commonly refers to a domain name, a human-readable address of a resource on the Internet assigned within the Domain Name System. Domain names map to IP addresses using DNS. Terms like top-level domain and second-level domain are common; registration is managed by registries and registrars.

In biology, the three-domain system places life into Bacteria, Archaea, and Eukarya, a higher-rank classification than kingdoms. In other uses, domain of discourse in logic refers to the set of objects under discussion; in databases, data domains specify the allowable values for an attribute.

Other uses include geographic or jurisdictional domains, fields of knowledge, or areas of responsibility within organizations.