I just discovered Common Craft. It’s a great educational resource for all sorts of things (Chris posted a video by them a while back: here). They produce short videos that explain things to people like Twitter, or how to use LinkedIn, all in ultra-basic paper style. So now, the next time you have to explain what Twitter is, you can point that person to Common Craft. They cover a wide variety of topics too like Zombies (see below…no, really, you gotta see it).
Zombies in Plain English
Social Networking in Plain English
Twitter in Plain English
Wikis in Plain English