(astronomy) A star system consisting of a solitary star not gravitationally bound to other stars

(politics) A democratic parliamentary system of government, used by and modelled after the British parliament in Westminster.

(logic) A set of axioms and a set of inference rules which are jointly used to deduce tautologies, thereby providing proofs of them.

(physics, chemistry, engineering) A physical system whose interaction with its environment is limited to particular types of transfer, so that certain quantities are conserved within the system.

(physics) A system that does not interact with its surroundings. Depending on context this may mean that its total energy and/or momentum stay constant. In thermodynamics, isolated is usually used to indicate that the system's energy does not change. In mechanics it is used to indicate that the system's momentum does not change.

(logic) The grouping of a formal language and a set of inference rules and/or axioms.

(ethics) A particular set of consistent ethical principles.

(mathematics, physics) A system which is time-dependent.

(artificial intelligence) A type of artificially intelligent software system, which stores expertise concerning some subject matter in a knowledge base and attempts to answer questions or solve problems in a manner which simulates the thought processes of a human expert.

(neuroanatomy) The autonomic nervous system.