Plain English Meaning
A tiny widened section at the end of each of the three loop-shaped tubes inside your inner ear. It holds the sensors that tell your brain when your head is turning.
Full Definition
A small bulb-shaped enlargement at one end of each of the three semicircular canals in the inner ear. It contains the cupula and sensory hair cells that detect angular acceleration of the head as fluid (endolymph) inside the canal moves past them.
Context Anchor
Seen in instrument flying discussions of the inner ear, especially when explaining why a pilot may feel a turn that does not match what the instruments show.
Derivation
From the Latin ampulla, meaning a small rounded flask or bottle. The name fits because this part of the canal is shaped like a tiny bulb compared to the narrow tube it sits at the end of.