Definition
A small wheel mounted at the rear of an airplane's fuselage that supports the tail on the ground. An airplane equipped with a tail-wheel (rather than a nose-wheel) sits with its nose pitched up while on the ground, with the two main wheels forward of the center of gravity and the tail-wheel behind it.
Plain English
A small wheel under the back of the airplane that holds the tail off the ground. Airplanes built this way sit nose-up when parked and rolling on the ground.
Context Anchor
Seen when studying or operating tail-wheel airplanes, especially during ground handling, takeoff, and landing discussions.
Derivation
Literally a wheel at the tail. The term is descriptive: it names the location of the wheel. It is worth knowing that this layout is also called 'conventional gear' because it was the standard arrangement on most early airplanes, before nose-wheel (tricycle) gear became common.
Why Pilots Care
Tail-wheel airplanes need special handling on the ground to avoid ground loops and propeller damage, and they behave differently during takeoff and landing than tricycle-gear planes.
Intuition Check
Do not read tail-wheel as just any rear wheel. In this context, it means the landing gear wheel at the tail of an airplane, and it affects how the airplane behaves on the ground.
Example Sentence 1
Before flying the Piper Cub, she completed her tail-wheel endorsement with a CFI.
Example Sentence 2
During the landing rollout in a tail-wheel airplane the pilot must stay ready to correct for any tendency to swing left or right.