A pane is a piece of glass, especially one that fits into a window frame. If you hit your baseball through your neighbors' kitchen window, you'll probably owe them a new pane. Panes are almost always made of glass, although occasionally they're some other translucent material.

The rain had been drumming on our window pane all night. All the other window panes would filter the light of the sun through their own distinctive designs. The status of a worker was signalled by the number of panes in his windows and the shape of door panels.

a panel, as of a door, wall, etc. 3. any of the flat sides, or faces, as of a nut, bolt head, cut diamond, etc.