Prime Rate

What Does Prime Rate Mean?
The interest rate that commercial banks charge their most credit-worthy customers. Generally a bank's best customers consist of large corporations. The prime interest rate, or prime lending rate, is largely determined by the federal funds rate, which is the overnight rate which banks lend to one another. The prime rate is also important for retail customers, as the prime rate directly affects the lending rates which are available for mortgage, small business and personal loans.

Investopedia explains Prime Rate
Default risk is the main determiner of the interest rate a bank will charge a borrower. Because a bank's best customers have little chance of defaulting, the bank can charge them a rate that is lower than the rate that would be charged to a customer who has a higher likelihood of defaulting on a loan.