The Federal Reserve Board provides this definition of the discount rate: 'Officially the primary credit rate, it is the interest rate at which an eligible depository institution may borrow funds, typically for a short period, directly from a Federal Reserve Bank'.
More detailed explanation of the discount rate can be found on The Discount Rate page on the Federal Reserve Board website and in Chapter 3 of The Federal Reserve System: Purposes and Functions
Sources for the Discount Rate
International Financial Statistics
Figures for the discount rate (end of period) are published in the International Monetary Fund publication 'International Financial Statistics' which is published monthly. This provides 9 months statistics for the discount rate (end of period). The ICAEW Library & Information Service holds the monthly edition of 'International Financial Statistics' back to January 2007 (with monthly figures for the discount rate back to March 2006 and quarterly figures back to Quarter 4 2004).
International Financial Statistics Yearbook
The yearbook provides annual figures for the standard discount rate. The ICAEW Library & Information Service holds copies of the 'International Financial Statistics Yearbook' going back to 1998 (with annual figures for the discount rate back to 1968).
Federal Reserve Statistical Releases
The Federal Reserve provides a historic table of Selected Interest Rates (H.15) which includes the Discount window primary credit. The archive of available rates includes daily, monthly and annual figures back to 9th January 2003 (the date that the discount rate switched to the rate of primary credit from the rate of adjustment credit).
Historical figures for the adjustment credit rate (1955 to 8th January 2003) are also included in the table of Selected Interest Rates (H.15).
See also
Knowledge Guide to Bank Base rates: UK