Final answer:
A security deposit is conditionally refundable, while a fee is not.
Step-by-step explanation:
The fundamental difference between a security deposit and a fee is that one is conditionally refundable, while the other is not. A security deposit is typically a refundable amount of money paid upfront by a tenant to a landlord to cover any potential damages to the rental property.
It serves as a form of insurance for the landlord in case the tenant causes any harm or fails to fulfill their obligations. On the other hand, a fee is a non-refundable payment that is usually charged for specific services or amenities, such as application fees, pet fees, or late payment fees.