"Something we didn't know we needed until we had it" - Biz Stone   

This is a great interview (with Colbert they're all great) with the co-founder of Twitter, Biz Stone.  Twitter is basically a way to keep in touch with people quickly and easily via text message and the twitter site.  You can constantly update friends and family on what you are doing while also receiving messages from the people you choose.  Messages are limited to 140 characters due to the fact that 160 characters is max for a text message (leaving 20 characters for a username).  And spaces count too!  This results in users coming up with creative ways to condense long messages.  140 characters takes you about halfway through the second sentence of this paragraph to get an idea of how short a Twitter message is... There have been rumors that Google is interested in buying Twitter at a price of around $1 Billion.  Currently it's not a profitable company, however the fact that there are around 11 million registered users does create a ton of value.  Demi Moore even stopped a woman's suicide attempt using Twitter.  Now go tell someone what you're doing.

Google Rumor

Demi Moore saving lives with Twitter