term:

Overage

overage n

: an amount exceeding a certain sum or quantity: as
a : a percentage of the amount of sales grossed by a retail store that is paid under the terms of a lease in addition to a fixed rent
b : an amount by which a payment or cost exceeds an expected or budgeted amount
c : surplus

Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.