Double-hung window
A window with two sashes that slide vertically within a frame. It came into use in the late 17th century, alongside the rise of masonry wall construction, and became popular in British aristocratic mansions and urban residences. Easy to adjust, it provides good ventilation. Also called hung sash window, vertically sliding sash window, or guillotine window. If only the lower sash is operable while the upper remains fixed, it is called a single-hung window.