my definition: the chip inside a video camera, that converts optical information into electronic bits suitable for computer processing and transmission
If you don't trust me, http://en.wikipedia.org/wiki/CCD says:
When a photon strikes an atom, it can elevate an electron to a higher energy level, in some cases freeing the electron from the atom. When light strikes the CCD surface, it frees electrons to move around and they accumulate in the capacitors. Those electrons are shifted along the CCD by regular electronic pulses and "counted" by a circuit which dumps the electrons from each pixel in turn into a capacitor and measures and amplifies the voltage across it, then empties the capacitor. This gives an effective black & white image of how much light has fallen on each individual pixel.