A pane is a single piece of glass that fits into a window frame. You can think of it like one slice of a pizza.
When you hear someone talk about panes, they probably mean windows or doors with glass in them. Think about your house – there are probably several panes of glass letting light and air in. A car windshield has many panes too. If someone says their favorite window has three panes, it means the glass is divided into two sections by a middle piece, often for design reasons. Sometimes people talk about a single pane shattering or getting broken – that means just one piece of glass cracks or falls apart.
An individual sheet of glass in a window, door, etc.
The (often spherical) end of the head of a hammer opposite the main hammering end.
