Here is a quotation on what bitcoins are:
Bitcoin is a new kind of money. It's the first decentralised electronic currency not controlled by a single organisation or government. Its an open source project, and it is used by more than 100,000 people. All over the world people are trading hundreds of thousands of dollars worth of bitcoin every day with no middle man and no credit card companies. Its a start-up currency which has never happened before.
Bitcoin is the first digital currency that is completely distributed. The network is made up of users like yourself so no bank or payment processor is required between you and whoever you're trading with. This decentralisation is the basis for Bitcoin's security and freedom.
Email let us send letters for free, anywhere in the world. Skype lets us make phone and video calls for free, anywhere in the world. Now there's bitcoin. Bitcoin lets you send money to anyone online, anywhere in the world for less then a cent per transaction! Bitcoin is a community run system not controlled by any bank or government. There's no Wall-Street banker getting rich by standing between you and the people you want to send and receive money from
Bitcoin is more efficient than all competing currencies. This will drive its adoption in the same way computers were adopted, in that computers made people more efficient in competing in the marketplace. Of course the early adopters will become rich, and I think they deserve it for having played a key role in the development of Bitcoin. A currency has value by it being widely used. Bitcoin is a startup currency with a deflationary bootstrapping economy. Their use spreads by providing the speculator incentive.
Bitcoin is going to be the biggest opportunity for innovation that the world has seen since the industrial revolution. An idea whose time has come.