While the term "sash" technically refers to any wooden framed window pane, the over/under style of window common in American architecture and known as a single- or double-hung window is commonly referred to as a sash window. Casement windows are broken into two groups as well. French casements open on hinges on both sides, while a crank casement pivots on a pin at the top and bottom of one side.
A single-hung sash is an over/under window with two panes. The upper pane, or sash, is fixed in place and does not open. The lower half of the window raises to open and lowers to close. The single moving pane is what gives the window its name. This style is typically found in smaller windows and is common in vinyl and aluminium replacements. The movement of the window is governed by pulleys and a counterweight.
Similar in style to its simpler cousin, the double-hung sash has two moving sashes. The upper sash can be drawn down to open, while the lower sash rises to open and drops to close, as with the single-hung sash. The movement is controlled by a double counterweight system, or springs in newer windows. These counterweight systems are housed in compartments beside the window, inside the frame or the wall.
French casement windows are very similar to French doors, in that they have two hinged panels that meet in a vertical joint in the centre of the window and are hinged to the jambs. These windows can have single or multiple panes of glass in each side. Traditional French casements are divided light, meaning they have more than one pane on each side. French casements can be driven mechanically with a crank, although many open and close freely on their hinges, much like traditional doors.
Single-sash casements have been used for centuries and were very common in "modern" architecture of the first half of the 20th century. Like French casements, they pivot open, rather than sliding, and they can be hung on traditional pin hinges or pivots mounted in the top and bottom of the frame. Most single casements are crank casements. Crank casements are opened with a mechanical screw crank, which typically has a handle on the inside of the sill, or to one side, that cranks one way to open and the opposite direction to close.