Balance Transfer
Definition
A balance transfer moves debt from one credit card to another, usually to take up a lower promotional rate. The new card clears the old balance and you repay the new card instead.
Promotional periods are commonly quoted at 0% for a fixed number of months, after which the standard rate applies to whatever is left.
Most transfers carry a fee, often a percentage of the amount moved, added to the new balance. That fee is what makes the arithmetic worth checking rather than assuming.
The saving comes from clearing the balance inside the promotional window. Anything still outstanding when it ends reverts to the ordinary rate.