what does the window mentioned above refer to?
It is a membrane-covered opening from the middle ear to the cochlea of the inner ear.
Oval window
The oval window (or fenestra vestibuli) is a membrane-covered opening from the middle ear to the cochlea of the inner ear.

where is the smallest bone in your body located In the middle ear. does the bone have a name? Yes, stapes or stirrup. what is its function? It transmits sound vibrations from the incus to the oval window.
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Oval window [SEP] Introduction
It is occupied by the base of the stapes, the circumference of which is fixed by the annular ligament to the margin of the foramen.