What the @#!$ is a hashtag? On Twitteria Lane, it's when you put a # in front of a word to facilitate real-time searching. So this thing I like about Twitter is actually two things.
1. By using a hashtag, you can easily search Twitter for a real-time list of twerps from everyone in the entire land of Twit who is intentionally discussing a topic in installments of fewer than 140 characters. If you want to discuss So You Think You Can Dance, you simply add the #sytycd hashtag to your dia-twibe, and anyone perusing an active search of that topic via Twitter's search feature or TweetDeck or any of the twillions of other Twitter-related applications.
And unlike Facebook or MySpace, you aren't just discussing with your friends, you're tweeting it up with all of Twitter. Everybody is gathered around one giant water cooler.
2. The hashtag also brings more practical usage to yet another rarely used character on the keyboard. For quite awhile, @ was reigning as the otherwise-useless symbol du jour, but # has taken its rightful place among the inner circle.
It's not just pound or number, anymore, baby. Make way for #, the hash master.