In place of the film used in conventional film cameras, digital cameras incorporate an electronic component known as an image sensor. Most digital cameras are equipped with the image sensor known as a CCD, a semiconductor sensor that converts light into electrical signals. CCDs are made up of tiny elements known as pixels. Expressions such as "2-megapixel" and "4-megapixel" refer to the number of pixels comprising the CCD of a camera. Each pixel is in fact a tiny photodiode that is sensitive to light and becomes electrically charged in accordance with the strength of light that strikes it. These electrical charges are relayed much like buckets of water in a bucket line, to eventually be converted into electrical signals.