An Internet media type, originally called a MIME type after MIME (Multipurpose Internet Mail Extensions) and sometimes a Content-type after the name of a header in several protocols whose value is such a type, is a two-part identifier for file formats on the Internet. The identifiers were originally defined in RFC 2046 for use in e-mail sent through SMTP, but their use has expanded to other protocols such as HTTP, RTP and SIP. There are many predefined MIME types, such as GIF graphics files and PostScript files. It is also possible to define your own MIME types.