(education, historical) The system of home study established in connection with the summer schools assembled at Chautauqua, New York, by the Methodist Episcopal bishop John Heyl Vincent.

(historical) A system used by the US Navy in the late 19th century to enable ship-to-ship communications at night. Each installation used a series of eight double lamps (four red and four white) hung from a mast and used to transmit visual codes.

A voting system.

(historical) A haulage system for canal boats, in which an electric locomotive running on a monorail has its adhesion materially increased by the pull of the tow rope on a series of inclined gripping wheels.

(physics) The portion of the physical universe chosen for analysis, with everything outside the system known as the environment.

A complete set of institutions, political organizations, interest groups (such as political parties, trade unions, lobby groups), the relationships between those institutions and the political norms and rules that govern their functions (constitution, election law).

(history) A particular system of measuring mass and volume.

(computing) A way programming language classifies values and expressions into types, how it can manipulate those types and how they interact.

(anatomy) The system of organs serving for respiration.

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