Hopper windows are a type of window closely related to casement windows and awning windows. All three of these open into (or out from) the room, opening on hinges rather than sliding or lifting.

Hopper windows are specifically those which are hinged on the bottom, opening at the top. The primary advantage to a hopper window is its use as a basement window, as these tend to be close to head-height on the inside and close to the ground on the outside of the house. Having the opening at the top of the window rather than the bottom (as it would be with an awning window) means that there are no sharp corners hanging down to whack you in the head, and it helps prevent leaves, dust, and trash that might be blown along the ground from blowing right into your basement.

On the downside, if they open outwards, they will funnel rain into your house. The window latch may also be too high to conveniently reach. You really gotta think about your windows.

As with awning and casement windows, hopper windows are energy efficient. The compression seal of these windows seals tighter than is possible for the sliding seals in traditional windows, keeping heat/air conditioning in, and the elements out.