What is "vestibule of the ear"

Vestibule \Ves"ti*bule\, n. [L. vestibulum, of uncertain origin: cf. F. vestibule.] The porch or entrance into a house; a hall or antechamber next the entrance; a lobby; a porch; a hall.

Vestibule of the ear. (Anat.) See under Ear.

Vestibule of the vulva (Anat.), a triangular space between the nymph[ae], in which the orifice of the urethra is situated.

Vestibule train (Railroads), a train of passenger cars having the space between the end doors of adjacent cars inclosed, so as to admit of leaving the doors open to provide for intercommunication between all the cars.

Syn: Hall; passage.

Usage: Vestibule, Hall, Passage. A vestibule is a small apartment within the doors of a building. A hall is the first large apartment beyond the vestibule, and, in the United States, is often long and narrow, serving as a passage to the several apartments. In England, the hall is generally square or oblong, and a long, narrow space of entrance is called a passage, not a hall, as in America. Vestibule is often used in a figurative sense to denote a place of entrance. ``The citizens of Rome placed the images of their ancestors in the vestibules of their houses.''
--Bolingbroke

n. the central cavity of the bony labyrinth of the ear

The vestibule is the central part of the bony labyrinth, and is situated medial to the eardrum (tympanic cavity), behind the cochlea, and in front of the semicircular canals.

The etymology comes from the Latin vestibulum, literally an entrance hall.