(anatomy) The system through which digestive waste is removed from the body.

(logic) A set of axioms from which theorems can be derived.

(logic) A formal system.

(computing) An old computer system or application program that continues to be used because the user (typically an organization) does not want to replace or redesign it.

(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.