Prime Rate - the Fed-set rate we all know and love. Few first mortgages are set to this-but home equity lines of credit almost always are
LIBOR - London InterBank Offered Rate - based on the interest rates at which banks offer to lend unsecured funds to other banks in the London wholesale (or "interbank") money market, usually US Dollars.
COFI - Cost of Funds Index - a regional average of interest expenses incurred by financial institutions, which in turn is used as a base for calculating variable-rate loans.
The Fed sets the Fed Funds Rate, banks set the Prime Rate.