I think Lee Lefever over at Common Craft does a mighty fine job of explaining Social Media (in plain English… as he always does):
If you like, here’s the direct link to the Common Craft video: Social Media in Plain English.
Just What Is Social Media Anyway?
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Never another podcast episode or article 
I love it! It’s crazy how we have to “dumb” things down to make it understandable but since it’s a new concept, it helps explain this to new people trying to understand digital marketing for the first time. Keep me posted for new videos from them.