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.
It belongs to TrueType and OpenType font formats and has analog compression that stores rendering technology. In WOFF it’s possible to store individual metadata with font info. It’s been used since 2010 for the main purpose of storing and transferring fonts on the Internet. It was developed by the Mozilla Foundation.