French Window is used where there is a space of about 6 to 8 feet A good Example is terrace or mini terrace. There are about 5 to 6 shutters out of which the side shutters are fixed (they dont move). Width size of these fixed shutters is 1 to 1.5 ft from which you can see outside. The middle shutters(3 or 4) are kept open so that you get maximum air and light.
You can put designer glass or transparent glass to these windows. This is the difference between normal window and french window.
The cost of window increases as per the size. Quantity of grill or wood is more compared to normal window. So the price increases. You can make a sit out in your room and a french window can be made from floor level.