A Louvred Window/Door is a framework of wood or metal fitted with fixed or movable horizontal slats of glass, acrylic, or wood for admitting air and light and shedding rain while preserving privacy. The louvers are locked together onto a track, so that they may be tilted open and shut in unison, to control airflow through the window. They are usually controlled by a crank mechanism. It is impossible to achieve a good seal between panes. It is also very hard to secure this design, as the slats are easily and silently removed. Being relatively weak structures, they are most commonly used for wardrobes and drying rooms, where security is of less importance than good ventilation.

WIKIPEDIA ENTRY FOR LOUVER.