(astronomy) A method of stellar classification in which stars are assigned Greek letters (α, β, γ, etc.) in decreasing order of brightness.

A mathematical model of a system based on the use of a linear operator.

(anatomy) The part of blood circulation which carries oxygenated blood away from the heart, to the body, and returns deoxygenated blood back to the heart.

(computing) The software associated with an operating system and supporting utilities, database systems etc.

(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.

(mathematics) A numerical system of counting in tens.

plural of solar system

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

dynamical system