Formerly known as MIME (Multipurpose Internet Mail Extension) types. These identify different types of files allowing software to handle them correctly. Puppy uses the standard provided by freedesktop.org.

When making a non-standard MIME-type use x- in the MIME-type name, for example application/x-tmd for a TextMaker document (registered ones are at www.iana.org/assignments/media-types/ IANA.org assigned media-types).

How To Add MIME Type
How to Associate Files to programs
Microsoft Office MIME-types
shared-mime-info - MIME-Type descriptions from freedekstop.org
freedesktop.org - open standard for linux
www.iana.org/assignments/media-types/ IANA.org assigned media-types
MIME Types and File Extensions
WikiPedia:Internet_media_type
Mime icons for ROX-Filer thread