This category lists various types of file formats used for storing palette information. A palette is a mapping between a number (typically between 0 and 255 inclusive) and the actual colour to draw when that number is encountered, for example by assigning colour 0 to black, colour 1 to yellow, colour 255 to magenta, or whatever set of colours suits the image best. Palettes typically contain a list of red, green and blue intensity levels for each colour to display.
Palettes are required as the display hardware in this era could only display a limited number of colours at the same time. For example VGA displays are capable of showing 262,144 possible colours, but of these, only 256 can be displayed on the screen at any one time. A palette is used to select which of the 262,144 colours will fill the 256 available slots.
Because of the close association between palettes and images, many images store the palette internally, in which case it won't be listed in these categories (details about these palettes are contained in the format description of the image itself.) Only separate, independent storage of a palette warrants an entry here (for example when a game uses only a handful of palettes across all images, each palette is often stored independently of any particular image.)