fee
A set amount of money you pay for a service.
A fee is a fixed amount of money charged for a service or privilege. When you go to a doctor, your parents pay a fee for the appointment. When you enter a national park, there's often an entrance fee. When you return a library book late, you might owe a late fee.
Fees differ from prices in an important way. When you buy something at a store, you pay its price: what that item costs. But a fee is payment for something less tangible, like someone's professional time, the use of a facility, or permission to do something. Your piano teacher charges a fee for lessons. A lawyer charges a fee for legal advice. Your school might charge an activity fee to help cover the cost of field trips and supplies.
Some fees are reasonable and expected, covering real costs of services. But others can feel frustrating: imagine saving up to buy concert tickets, only to discover that “convenience fees” and “processing fees” add $20 to the price. That's why people sometimes complain about hidden fees, charges that weren't clearly explained upfront. When fees are fair and transparent, they help organizations cover their costs. When they're sneaky or excessive, they can feel like a way to take extra money from people who have no choice but to pay.