A media type (also known as a MIME type) is a two-part identifier for file formats and format contents transmitted on the Internet. The Internet Assigned Numbers Authority (IANA) is the official authority for the standardization and publication of these classifications. Media types were originally defined in Request for Comments RFC 2045 (MIME) Part One: Format of Internet Message Bodies (Nov 1996) in November 1996 as a part of MIME (Multipurpose Internet Mail Extensions) specification, for denoting type of email message content and attachments; hence the original name, MIME type. Media types are also used by other internet protocols such as HTTP and document file formats such as HTML, for similar purposes.
A list of supported MIME Types can be found at /etc/mime.types
Naming
A media type consists of a type and a subtype, which is further structured into a tree. A media type can optionally define a suffix and parameters:
type "/" [tree "."] subtype ["+" suffix]* [";" parameter]
As of November 1996, the registered types were: application, audio, image, message, multipart, text and video. By December 2020, the registered types included the foregoing, plus font, example, and model.
An unofficial top-level name in common use is chemical.
As an example, an HTML file might be designated text/html; charset=UTF-8. In this example, text is the type, html is the subtype, and charset=UTF-8 is an optional parameter indicating the character encoding.
A subtype typically consists of a media format, but it may or must also contain other content, such as a tree prefix, producer, product or suffix, according to the different rules in registration trees.
Types, subtypes, and parameter names are case-insensitive. Parameter values are usually case-sensitive, but may be interpreted in a case-insensitive fashion depending on the intended use.