Final answer:
An 'Acceleration' clause refers to the contractual provision allowing a lender to require a borrower to repay all of an outstanding loan if certain conditions are violated.
Step-by-step explanation:
An 'Acceleration' clause most nearly means to speed up payment of an overdue debt. This clause is often found in loan agreements or contracts and allows the lender to demand immediate repayment of the entire outstanding balance if certain conditions are met, such as missing a series of payments. It is a financial term and has little to do with the physical concept of acceleration, which relates to the change in velocity of an object.