Domain

Domain has several meanings:

General

some kind of territory, such as (for example) a demesne or a realm
synonymous with a metaphorical field, e.g. "the domain of computer science"
a field of study
public domain, a body of works and knowledge without proprietary interest
domain of discourse in symbolic logic
atomic domain - a domain whose elements class as indivisible units
eminent domain, the power of government to confiscate private property for public use
in several Commonwealth countries, the name for parkland made available for public use by the monarch or their representative, the Governor. Examples include:
- The Domain, Sydney: a large open space near the central business district of Sydney, Australia
- King's Domain, Melbourne: in Victoria, Australia
- Queens Domain, Hobart: in Tasmania, Australia
- The Domain, Auckland: a large inner-city park in Auckland, New Zealand containing an ancient volcano and the War Memorial Museum

in biology, a domain forms a subdivision even larger than a kingdom
in biochemistry and protein science, a domain is an autonomously folding functional module of a protein
in physics a domain comprises a region of a solid inside which a property is uniform (for example magnetic domain in ferromagnetism)

In mathematics domain can refer to:

In information technology, the term domain can refer to:

a machine or virtual host on the Internet; do not confuse the name of a domain - its "domain name" - with the domain itself
a Windows Server domain, a centrally-managed group of computers using the Windows operating-system
a broadcast domain in computer networking
an application domain - the kinds of purposes for which users use a software system
a software engineering domain - a field of study that defines a set of common requirements, terminology, and functionality for any software program constructed to solve a problem in that field. See also domain-specific programming languages.
a Common Language Runtime application domain, a mechanism for separating executed applications (similar to a process)
In Database Theory, a Domain is a set of all permitted atomic values.
a workstation operating system called Domain/OS.

The original etymological implication of the word domain carries the idea of "something ruled". Compare and contrast dominion, domination, dominant and demesne.