The singular media and its plural medias seem to have originated in the field of advertising over 70 years ago; they are still so used without stigma in that specialized field. In most other applications media is used as a plural of medium. The popularity of the word in references to the agencies of mass communication is leading to the formation of a mass noun, construed as a singular <there's no basis for it. You know, the news media gets on to something — Edwin Meese 3d><the media is less interested in the party's policies — James Lewis, Guardian Weekly>. This use is not as well established as the mass-noun use of data and is likely to incur criticism especially in writing.