The price that a person must pay in order acquire purchasing power now rather than in the future is called

the interest rate.

Explanation:

The interest rate -

It refers to the due money for the principal amount for the borrowing process, is referred to as the interest rate.

The amount of interest is directly proportional to the principal amount.

i. e.,

more the principle amount, more would be the interest rate, and vice versa.

The interest rate applied on the yearly basis, is refers to as the annual interest rate.

Hence, from the given statement of the question,

The correct answer is the interest rate.