Definitions for "Indexed Colour"
Reduced colour mapping, 8 bit or less; done to reduce images to their smallest size. Commonly used for images placed on Internet pages. The 256-colour palette are also mapped for best results on the Internet, taking into account the differences between the Windows and Macintosh colour palettes.
One method of displaying or encoding colours in an image file, 8 bit or less. Indexing assigns colour values from the entire gamut to a relatively small array of colour indexes. This array of colours becomes the colour table from which all colours in the image are selected. Done to reduce images to their smallest size.
In PhotoShop, an image mode in which there is only one channel and a colour table that can contain up to 256 colours. All the colours in an Indexed colour image are displayed on its table--unlike an image in any other mode.