Nozzle

It is possible that you already have a good idea of what a nozzle is, but since it is a word with two 'z's in it, it deserves its place here. A nozzle is a mechanical device designed to control the direction or characteristics of a fluid flow as it exits an enclosed chamber via an opening. They have different meanings and applications in a wide variety of technologies, but the principal use of nozzles in space industry is in optimising the expansion ratio of exhaust products from the combustion chambers of rocket engines. The concepts apply equally to solid and liquid fueled engines. Nozzles come in a wide variety of sizes, usually integrate active cooling components, and are often mounted on gimballed mechanisms to aid guidance controls.

Rocket nozzle