Two or more human beings cannot communicate directly. That is, they cannot transfer thoughts between each other minds just like that. Instead, they have to communicate indirectly, through something else in the middle. The bit in the middle is called a medium (plural media). Indeed, any time information has to flow between a data source and one or more data sinks, the information has to flow through a medium. Otherwise, the source and the destination would be the same entity.
Examples of media:
Compare ParaLanguage, WhatIsCommunication, MassMedia, HyperMedium
I'm no way a media expert, but something seems wrong with the list above. It mixes media like Paper, Webpages and Television with content transported on the media, like "Music" or "Speech". I also think that people can communicate "directly", because it doesn't make sense in this context to think of air as a medium for spoken language. A medium introduces the ability to store the content and maybe reproduce or multiply it. Another term useful in this context may be the "media format" (German Medienformat, don't know what it's in English), e. g. the content "Music" might be transported using the media format "Superstar show" through the media "Television". I think that a wiki is a "media format" within the media "World Wide Web". A text about WhatIsaMedium might be printed on the medium "Paper" or written into the medium "Webpage" using the media format of an "Essay" or a "Wikipage". Language seems to be defined on an even lower level. Different languages may be used over the same medium, so I think BodyLanguage is not a medium.
One might try a hierarchy:
Just a few thoughts. -- HelmutLeitner
An interesting dissertation about types of media: Davis Fougler's "Medium as Process", here: . See especially the "Typology of Media" in ch. 8.