definition
strict definition
hopper
An openable window hinged along its bottom edge, allowing the rest of the pane to swing about that edge.
A hopper window is an openable window which is hinged at the bottom, enabling it to swing open like a drawbridge being lowered.
The lower edge supplies the hinge axis. An awning window has the corresponding hinge at the top.
A tilt window is hinged in the middle. The location of the hinge distinguishes it from the bottom-hinged hopper.