Unsecured loans are sometimes called 'signature loans' because the bank has nothing but your signature -- they can't take possession of your house, car, or other belongings. However, they can report you to the credit reporting companies and ding up your credit.
For people who don't have any collateral to pledge, an unsecured loan can be attractive. Be aware that there is more risk to the bank, so the interest rates on unsecured loans are typically higher.
Peer to peer lending has made it easier to get unsecured loans at a reasonable rate.