Content types denote what kind of file is being transmitted over the Web. Files are tagged according to the MIME standard, using type designations like text/plain, text/html, image/jpeg, or video/quicktime. Type designations that are not officially registered have an x- prefix, like audio/x-midi or application/x-javascript. The Internet Assigned Numbers Authority (IANA) maintains the official registry of content types.

They are sometimes referred to as mime types, maybe that is causing the confusion?

MIME content types are the standard way of denoting the nature of a file transmitted over the Web. Originally, the e-mail protocol supported only plain text. MIME (Multipurpose Internet Mail Extensions) were originally devised to tag e-mail with content types, allowing people to send images, audio, video, programs or other sorts of files. Over time, these content types were used to label content types in many other Internet protocols.

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