This explains it better than anyone can write it here (plus it has photos): http://en.wikipedia.org/wiki/Sash_window

The image is the easiest way to understand a new concept! https://www.google.dz/search?q=velo+stationnaire&client=firefox-beta&hs=9iK&rls=org.mozilla:fr:official&channel=sb&tbm=isch&tbo=u&source=univ&sa=X&ei=cLk6U7a0I6mo4AS00YGQDA&ved=0CEcQsAQ&biw=1366&bih=657#channel=sb&q=wide-sash+window&rls=org.mozilla:fr:official&spell=1&tbm=isch Copy this link and paste it in your browser,...D; Good luck

a wide window which can slide vertically to let in air

size method where u can distroy windows.......

Hi! It is more relevant to older buildings which had tall ceilings and therefore taller windows, basically it means that the bottom half of the window could slide up to superimpose itself over the upper half and alternatively, vice versa for the top half to slide down over the bottom half, it's a good way to control the ventilation whilst allowing more light into the building. Hope it helps, regards, John