Twin-engined describes an aircraft that has two engines. It is an adjective and it goes in front of the noun: a twin-engined plane, a twin-engined helicopter. You do not normally say "the plane is twin-engined" after the verb — it sounds odd; people say "the plane has two engines" instead.

Why have a special word for it? Because in flying, the number of engines is a serious matter. A plane with one engine is in real trouble if that engine stops. A twin-engined plane can usually keep flying on the one that is left and land safely, so the number is part of how the aircraft is described, licensed and flown. Pilots are trained and rated for single-engined or twin-engined aircraft separately. In news reports of a crash you will often read "a twin-engined light aircraft", because that detail tells the reader something real about the plane.

The word belongs mostly to aviation writing, news reports and people interested in planes; it is not everyday conversation. You will meet the same shape in other words: twin-engined is one of a family — single-engined, four-engined, jet-engined. British writers spell it twin-engined; American writers often write twin-engine, with no -d. Both are correct in their own place. Note also that it is used for boats and cars sometimes, but planes are where it lives.