Balance Transfer Fee

Quick answer: A one-time fee charged when transferring a balance from another card, usually 3-5% of the transferred amount.

Math the fee against your interest savings before transferring. On a $5,000 balance with a 5% BT fee ($250) and a 15-month 0% intro APR, you save real money only if the balance you'd carry would have accrued more than $250 in interest in 15 months. For small balances, the fee often eats the savings.