"Screencasts are basically little movies you create on your computer. In most cases, they are movies of your computer." The recent Loose Wire column in The Wall Street Journal is everything about Screencasting:
I'd quite understand if you feel you've heard enough about new gizmos, programs and paradigm-shifting delivery mechanisms. A lot of it may sound great to geeks, but to ordinary Joes who just want to get through their business day without their computer crashing, a lot of it may seem a little, well, hyped.

Screencasts are really simple to grasp. And in some ways they're not new. But I, and a few thousand other people, think they represent a great way to leverage the computer to train, educate, entertain, preach and otherwise engage other people in a very simple way. Something the Internet and computers have so far largely failed to do.
A subscription is required to read the full WSJ article but the story author, Jeremy Wagstaff, has posted some useful links to Screencasting software and resources on the LOOSE wire blog.