A sunroof is a panel in the roof of a car that can be opened or slid back, so that air and light come in from above. Some slide open, some only tilt up at the back, and some are made of glass so light comes through even when they are shut. In car advertisements you will also meet moonroof (an American word, usually for the glass kind) and panoramic sunroof (a big one stretching over the back seats too) — for everyday talk, sunroof covers them all. It is one word, and it is countable: a sunroof, two sunroofs. Note that we say a car 'has a sunroof' and that you 'open' or 'close' it, and that the roof of a house does not have one — this word belongs to cars.