What is Twitter??

It seems like a new craze is sweeping the nation: Twitter. But I really don't have a good grasp of what it is. It's changing facebook, it's allowing faster communication somehow, and everyone from politicians (President Obama, for example) to Rock stars seems to be using it. Twitter allows the user to post what they're feeling at any time of the day, as much as the want during the day, but it's limited to a certain number of characters. I never knew that the internet would really want to know what was going on at every second of my life, or even if they cared, so maybe Twitter is a tool for conversation? Or if chivalry and the feeling to want to know about other people besides ourselves is emerging? Who knows. Or is it just another blogging device or a facebook-esque tool? Enlighten me.