(historical) A system of prison discipline involving periods of confinement to one's cell, associated imprisonment under the mark system, restraint intermediate between imprisonment and freedom, and liberation on ticket of leave.

(historical) A system for identifying people by a physical description based upon anthropometric measurements, notes of markings, deformities, skin colour, impression of thumb lines, etc.

(baseball) A method of sharing playing time, whereby two players are selected to play a single defensive position.

(music) A method of musical composition based on mathematical processes, comprising theories of rhythm, harmony, melody, counterpoint, form, and semantics.

(computing) A person who oversees the day-to-day operation of a computer system

(science fiction) The Solar System

plural of file system

A particular gambling strategy used in roulette, involving working through a list of numbers that sum to a total.

plural of fly system

A system of theatrical rigging, using ropes, blocks, etc., allowing the stage crew to fly (hoist) components such as curtains, lights and scenery.