base rate

Noun

 * 1)   A benchmark interest rate, from which other interest rates are calculated; a policy rate.
 * On loans to higher-risk customers, the bank charges 5% above the base rate.
 * 1)  Especially, the interest rate at which the  lends money to commercial banks.
 * 2)   The background rate of occurrence of any phenomenon, which informs any logical analysis of its rate of occurrence under any subset of circumstances; especially, the proportion of individuals in a population who have a certain characteristic (e.g., trait, experience, circumstance), irrespective of any treatment effects in a treatment group of a scientific study.