mediatype

A mediatype, also known as a MIME type or Internet media type, is a standardized identifier used to describe the nature and format of a piece of data. It helps software determine how to handle, display, or process the content, and supports interoperability across systems and protocols such as email and the World Wide Web.

A mediatype has a two-part structure: a primary type and a subtype, separated by a slash. Examples include text/html, image/png, application/json, and video/mp4. Mediatypes may include parameters after the subtype, typically in the form key=value pairs separated by semicolons. Common parameters include charset for text types (for example, charset=utf-8) and boundary for multipart types. The name parameter and others are used in some contexts but are less universal.

Mediatypes are standardized and registered to promote a consistent vocabulary. The original MIME specifications in RFC 2045 and RFC 2046 established the concept for email, while the registry and more recent guidance are maintained by the IANA, with the authoritative list published as "IANA Media Types." The guidelines are complemented by related standards in HTTP, where the Content-Type header uses a mediatype to indicate how the body should be processed.

Practical use includes content negotiation, streaming, and proper handling by clients and servers. While many commonly used types are widely supported, new or vendor-specific types may be introduced and registered to ensure broad compatibility. Historical practice of using non-standard "x-" types has declined in favor of formal registrations.

See also MIME, HTTP content negotiation, and IANA media types registry.