David Wilcox just finished writing a glossary of social media aimed at helping non-techies understand terms that enthusiasts take for granted, like blog, wiki, tag, podcast, feed — and added some interpretation of why common words like conversation, culture, openness have particular importance.
The glossary comes in a short version and a long version. The latter may be of more interest to those more familiar with social media.
Wilcox would really welcome any comments and/or additions you can offer in the discussion tab.