Sash Windows

A sash window or hung sash window is made of one or more movable panels or "sashes" that form a frame to hold panes of glass, which are often separated from other panes (or "lights") by narrow muntins. Although any window with this style of glazing is technically "a sash", the term is used almost exclusively to refer to windows where the glazed panels are opened by sliding vertically, or horizontally in a style known as a "Yorkshire light", sliding sash, or sash and case (so called because the weights are concealed in a box case). The oldest surviving examples of sash windows were installed in England in the 1670^s.

Source : http://en.wikipedia.org/wiki/Sash_window