Do not change something while it is working.

(aeronautics) A device which warns the pilot that the aircraft may be in danger of collision with the ground.

(astronomy) A body in the Solar System other than a planet, dwarf planet or natural satellite.

An air conditioner where the inside-environment (evaporative) heat exchanger is separated by some distance from the outside-environment (condensing unit) heat exchanger.

(construction) A system of drains and moisture barriers used to regulate the hydrostatic pressure in the earth surrounding a below-grade structure.

(aviation) An onboard system used to avoid controlled flight into terrain (CFIT).

A backpack, worn on a space suit, that provides breathable oxygen and removes expelled carbon dioxide

(software) Synonym of nominative type system

(mathematics) The real number system adjoined with two extra symbols: ∞ and −∞, inheriting the ordering of the real number system, and defining −∞ to be less than any real number, and ∞ to be larger than any real number.

A system of railroad equipment designed to ensure safety by monitoring locations of trains and locomotives, providing analysis and reporting, and automation of track warrants and similar orders.