1 [data models] The smallest unit of information in an image or raster map, usually square or rectangular. Pixel is often used synonymously with cell.
2 [remote sensing] In remote sensing, the fundamental unit of data collection. A pixel is represented in a remotely sensed image as a cell in an array of data values.
3 [graphics computing] The smallest element of a display device, such as a video monitor, that can be independently assigned attributes, such as color and intensity. Pixel is an abbreviation for picture element.