Balance transfer credit cards allow you to transfer debt from one credit card provider to another and pay no interest on that debt for a set period.
Some of the leading deals give you 0% interest for as long as two years or even more.
You'll generally have to pay a balance transfer fee if you want a longer 0% period, which is a percentage of the total debt you are transferring. Typically, the longer the offer period, the higher the fee will be, but it's generally between 1% and 4%.