A pinhole camera is basically a camera without a lens and with a single small aperture. Its pretty much a light proof box with a small hole in the side. It almost emulates the human eye when in bright light by taking in light from a small hole and shows an inverted image the other side. A common use is to capture the movement of the sun over a ling period of time.
How to make one
The easiest way to make a pinhole camera would be to get a light proof box, put a pinhole in one side and a piece of film taped to the other end. A simple piece of cardboard as a shutter. The pin hole should be punched through a piece of tin foil or something similar, then this piece should be then taped to the inside behind the hole in the box.