A pixel (short for "picture element") is the smallest element of a digital image displayed on screen — a single dot of color within a larger grid of dots that combine to form a picture. The word "pixel" can refer to both the physical element on a monitor capable of displaying a single dot of color and to the digital data representing each dot within a raster image file. The more pixels in an image or monitor, the higher its resolution and the more detail it can display.
Computer monitors and other screens contain a matrix of thousands or even millions of pixels. An individual pixel displayed on a monitor is often too small to be seen by the naked eye, with some HiDPI monitors containing more than 200 pixels per inch. Each pixel on a screen consists of three smaller subpixels (one each for red, green, and blue) that mix light into a single color.
Every raster (or bitmap) image consists of a grid of square pixels. Each pixel only displays a single color; combining thousands (or millions) of pixels allows the colors in those individual dots to blend smoothly. How many possible colors a pixel can display is determined by the image's color depth — the number of bits it uses to store a single pixel. A color depth of 8 bits allows for 256 (28) possible color values, while a higher color depth of 24 bits allows each pixel to have one of more than 16 million (224) possible colors.