(metrology) A standard set of units of measurement for use in scientific literature worldwide. The newest and most widespread version of the metric system.

(computing) A system allowing hardware and software from different manufacturers to be used together seamlessly. / (physics) A system that can exchange both matter and energy with its surroundings.

The Sun and all the heavenly bodies that orbit around it, including the eight planets, their moons, the asteroids, and comets.

(computing, Internet) The distributed database, sometimes including all the supporting hardware or software infrastructure, the Internet uses to translate hostnames into IP addresses and provide other domain-related information.

(rare, organic chemistry) Any organic compound, in the form of a ring, that has the maximum number of noncumulative double bonds; e.g. benzene or indole.

An informal method of communication used to pass information to US citizens during emergencies.

(astronomy) The combined system or structure formed by all of the rings orbiting a planet

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

(aviation) A collection of radio navigation aids (always including a localizer and glideslope, and often one to three marker beacons as well) used by pilots for approach guidance to a specific airport runway, especially when visibility is limited.

(anatomy) A system of organs for the purpose of digesting food.