Sliding sash windows from Isis Windows
A sash window is made from one or more moveable panels or sashes forming a frame holding glass panes, often separated from others by glazing bars.
Almost always, the term refers to windows where the glazed panels are opened by sliding vertically, or horizontally, and these models have been found in English homes as far back as the 1670s.
The style is often found in Victorian and Georgian houses, and, in the classic arrangement, there are three panes across by two up on each of two sashes, giving a six by six window, although this isn’t set in stone.
To make the operation smoother, the weight of the glazed panel is typically balanced by a heavy weight or counter-weight hidden within the frame.