Type code

A type code is a mechanism used in pre-OS X versions of the Macintosh operating system to denote a file's format, in a manner similar to file extensions in other operating systems. Codes are limited to four characters. For example, the type code for a HyperCard stack is STAK; the type code of any application program is APPL.

Type codes are not readily accessible for users to manipulate, although they can be changed with certain software tools.

See also creator code.