Convenience Fee

When you use a credit card, it costs the merchant money. They have to fork over a certain amount of the purchase price to the credit card company as the cost for the card company letting them use the service. Usually, the merchant just eats this cost as the price of doing business. Accepting credit cards either increases the volume of purchases, or in the case of online retailers, might be one of the few ways to get paid at all (since cash or check isn't an option).

Other places might try to pass some of these costs onto the consumer. The euphemistically named "convenience fee" represents one method to accomplish this (you are being charged for the convenience of using the card).

Credit card companies have rules in place to limit these fees. After all, they don't want people discouraged from using the card. But there are loopholes in the rules, and some places just outright ignore the company's guidelines on these fees.

Convenience fees most often come up for big ticket items. A new water heater...your mortgage payment...that kind of thing.