Common Craft have produced a series of videos which explain many social media concepts in plain English. If you are new to social media, these short videos are a great place to start.
Social Media in Plain English
Blogs in Plain English
RSS in Plain English
Wikis in Plain English
Podcasting in Plain English
Twitter in Plain English
Twitter Search in Plain English
Online Photo Sharing in Plain English
Google Reader in Plain English
Social Networking in Plain English
LinkedIn in Plain English
Google Docs in Plain English
Social Bookmarking in Plain English