Why are groups of Morris dancers called "sides"?

And when they get together, do they sing "Which Side Are You On?"

Here's another word I learned recently: "backscatter." It's when you suddenly get a ton of messages in your inbox, all automatically generated, saying that an e-mail that you sent could not be delivered because it had an invalid address. Except you didn't send it. Some spammer did, and they sent it in your name.

It happened to me, and the IT department of the university where I work explained it.

There's some information at Yahoo News.