In math it would be a reciprocal. A reciprocal is simply one of a pair of numbers that, when multiplied together equal 1. To find the reciprocal of a whole number just turn it into a fraction in which the original number is the denominator and the numerator is 1. The reciprocal of 7 is 1. Hope this helps.
It can also be an adjustable mortage rate fixed for 7 years. Kidding of course but true.