This is a format for presenting fonts in PDF files that was initially conceived to store symbols in the Japanese and Chinese languages because it had a 16-bit structure and allowed for more precise adjustment. CID expands the the potential for PostScript by supporting languages that do not have a left-to-right orientation, and by supporting even a vertical mode of orientation.
This format is used to store background images in uncompressed form in the X Windows System user interface for remote server maintenance. It stores a 'dump' or screenshot of the window or background of the client program. It may include different colors depending on the capabilities of the graphics card that is used to create the XWD file.