PRIME RATE

low rate of interest charged by banks to large or preferred accounts

Prime rate is a term applied in many countries to a reference interest rate used by banks. The term originally indicated the rate at which banks lent to their most favoured customers, though this is no longer always the case. Some variable interest rates may be expressed as a percentage above or below prime rate.
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The interest rate at which banks lend to their best (prime) customers. Much more often than not, a bank's most creditworthy customers borrow at rates below the prime rate.