1. The cost in dollars for the use of money for a period of time or “rent” paid for the use of money. 2. The type and extent or having a portion, share or right in the ownership of something. Example: Lenders require payment of interest at a specified rate, to compensate for risk. deferment of benefits, inflation. and administrative burdens. Example: One may hold either a partial or fee simple interest in a property That interest entitles one to specific ownership rights..