File with a .MD extension contains a document in a plain text format but with markers formatting it – boldface, italics, headers, cut-ins or tables. It can be stored in a number of dialects of the Markdown language, witch differ among themselves. Files can be also stored with a .MARKDOWN extension.

The creator of Markdown is John Gruber, who is also an author of Perl – used to convert files into HTML, available at Daring Fireball website. MD files are used do write documentation and to control a version of software’s source code, for instance, in the widely popular GitHub platform.