More accurately, they are media types for the MIME which include many other specifications such as message formatting.

In the following quoted texts are excerpts from the RFC2046 document. Highlighting within such text is our own.

1. THE RFC2046 DOCUMENT

The five discrete top-level types with their subtypes are:

-	text	intended for documents conveying textual information
		Subtypes defined in the RFC2046 document are:
		. plain indicates plain text that 'is intended to be displayed "as-is", that is, no interpretation of embedded formatting commands, font attribute specifications, processing instructions, interpretation directives, or content markup should be necessary for proper display.' . richtext 'used for enriched text in forms where application software may enhance the appearance of the text, but such software must not be required in order to get the general idea of the content' . enriched is a revision of the richtext subtype
-	image	intended for image contents; rendering of documents containing such data require a special device such as a graphical display, a graphics printer or a fax machine.
		Subtypes defined in the documents are:
		. gif indicates an image in the GIF (Graphics Interchange Format) format . jpeg indicates an image in the JPEG (Joint Photographic Expert Group) format
-	audio	intended for aural documents; such documents need an audio output device (speaker or telephone) to be rendered
		One subtype was defined:
		. basic 'the content of the "audio/basic" subtype is single channel audio encoded using 8bit ISDN mu-law [PCM - Pulse Coded Modulation] at a sample rate of 8000 Hz.'
-	video	intended for documents that contain moving images; necessitates a device capable of rendering such images
		One subtype is defined
		. mpeg 'refers to video coded according to the MPEG (Moving Pictures Expert Group) standard' .
-	application	'to be used for data which do not fit in any of the other categories, and particularly for data to be processed by some type of application program... Expected uses for the "application" media type include file transfer, spreadsheets, data for mail-based scheduling systems, and languages for "active" (computational) material.'
		Two subtypes are defined:
		. octet-stream 'to be used in the case of uninterpreted binary data, in which case the simplest recommended action is to offer to write the information into a file for the user . postscript describes Postcript documents; necessitates a printer or software capable of processing the Postcript language; 'PostScript is a registered trademark of Adobe Systems, Inc. Use of the MIME media type "application/postscript" implies recognition of that trademark and all the rights it entails.'

The composite types are:

-	multipart	'data consisting of multiple entities of independent data types'
		Four subtypes are defined:
		. mixed specifies a generic set of mixed parts . alternative specifies a set of parts containing the same data in different types . parallel specifies a set of parts to be simultaneously displayed . digest specifies a set of parts each of which has a default type of "message/rfc822".
-	message	specifies a document containing encapsulated messages
		Three subtypes are defined:
		. rfc822 the encapsulated content is an RFC822 message as defined in the RFC 822 document -- these are essentially messages composed of a number of header fields, followed by a text body of ASCII characters. . partial specifies a partial RFC822 message -- intended for fragmented transmission of large message bodies . external-body for messages with large parts defined by reference to an external source

2. SOME COMMON SUBTYPES

Provision has been made for further subtypes to be added as new needs arise. A document by the IANA (Internet Assigned Numbers Authority), dated from October 16th, 2001 lists a number of registered subtypes of differents types.

Some of the better known subtypes are:

Text type

Image type

Audio type

Video type

Application type

Multipart type

Message type