Macintosh type/creator code
A Macintosh type code is a file format identifier primarily associated with classic Mac OS. It is in the form of a FourCC.
A creator code is similar, but identifies the application that created the file, and/or the application that should be used to open it. Often, the combination of both the creator code and type code is needed to denote, or to clarify, a file's format. Creator codes containing all lowercase letters are reserved for use by Apple. Developer creator codes must contain at least one upper case letter.
These codes are essentially the classic Mac OS version of a file extension. They are part of a file's standard metadata in Macintosh filesystems such as HFS. They are found in many Mac-specific archiving formats, often via Finder information.
