Investopedia defines the bank prime rate as "The interest rate that commercial banks charge their most credit-worthy customers. Generally a bank's best customers consist of large corporations."
The prime rate is a fairly good indicator of interest rates in general. Often if you apply for a variable rate loan it will be based on the prime rate + X%. For example a home equity loan may be cited as prime + 0.74% if you have very good credit.
From the data at the Fed site I made graphs of the historical rates over history. First lets look at the rates from 1955 to 2008.
Yeah the rates hit 20% range in the 1980's. The maximum was 21.5% in December 1980. The average rate was about 10.1% and the median rate was 9%. The minimum rate was 3.25% recorded on Dec. 2008 as well as back in August 1955.
Now lets chart just the last 20 years:
In this period the average rate was 7.2%, the median was 7.5%, the maximum was 11.5% and the low was 3.25%.