Brian Solis has raised the question, "What is social media," and has invited people who think about such things to collaborate with him on a wiki.I think this is likely to provoke an interesting conversation, but defining the term is not one of the issues I puzzle over.
To the best of my knowledge, Demo Executive Producer Chris Shipley (who really should blog more often), coined the phrase during a keynote talk kicking off Demo 05. She later used the term when I worked with her to produce the first BlogOn conference held that same year at C Berkeley.
As I recollect, Chris defined it as "anything that uses the internet to facilitate conversations." To be that is simple, clear and powerful. It does not need committee review. I have been pushing the term ever since I heard it from Chris and I have always preferred "social media" to the more loosely defined and poorly understood term "Web 2.0."