A fee is the cost of something, or the amount of money charged. You might need to pay a fee when you visit your favorite state park.
Clubs, national parks, and gyms all charge a fee to belong or to enter. There is also the fee that a professional charges for services, like the legal fee you pay when you hire an attorney or the fee you pay your dentist to clean your teeth. Fee has an Old French origin in the word fieu, "possession, holding, domain, or payment," from the Medieval Latin feodum, "land whose use is granted in return for service."