What is MIME Type
Multipurpose Internet Mail Extensions (MIME) is a series of internetl stands, the main purposes are to extend a standard method of email content delivery. Of course MIME is now using in more aspects, eg internet, communication, etc.
Standard MIME header includes MIME Version, Content-Type, Content-Disposition, Content-Transfer-Encoding, and other components. You can get more information about MIME from ietf website linked (RFC2045~RFC2047, RFC4288~RFC4289, etc ).
But we know we do not needs all of them when we use MIME in other project instead of email program. Furthermore we can expand its definition too.
Normally when we say about MIME type, it due to the Content-Type definitions. Then it will be simple to understand. Content-Type composed by two parts: main type/sub type. For example.
*.xml MIME type is: application/excel
*.json MIME type is: application/json
Because there are numerous types of files, so there is nobody or organization can give a complete definition, surpporting only a few types of file may be a good choice for all of us.