cid – Fonts defined by character identifier

CID-keyed fonts were developed by Adobe to handle character sets containing large numbers of glyphs, notably for East Asian languages (Chinese, Japanese, Korean, etc.). The glyphs are addressed by number rather than name, and organized into so-called collections.

Several of Adobe’s CID mapping files are distributed as part of ConTeXt. In TeX Live, they are in the directory texmf-dist/fonts/cid.

See the Wikipedia entry, among other places, for more information.