ISO9660 is standard filesystem used on read-only optical discs (mostly CD-ROM). The standard was based on earlier High Sierra Format (HSF), proposed for CD-ROMs in 1985, and, after several revisions, it was accepted as ISO9960:1998.
The format emphasizes portability (thus having pretty minimal features and very conservative file names standards) and sequential access (which favors disc devices with relatively slow rotation speed).
This page hosts a formal specification of ISO9660 CD filesystem using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.