Casement, hopper and awning windows are three variations of the same frame design, with the difference based on hinge location.
Casement windows have a hinge at the side; awning windows have hinges located at the top, and hopper windows are an inverted version of the awning windows with hinges located at the bottom.
These models provide higher energy-efficiency than that provided by gliding and double-hung windows.
They are particularly energy-efficient and provide excellent ventilation. They are also very air-tight.