It is defined as a series of equal payments occurring at equal intervals of time.

The term "annuity" accurately describes a series of equal payments made at regular intervals. This financial concept encompasses various forms of financial agreements, such as retirement savings plans or structured settlements, where consistent monetary amounts are received or paid over a predefined period.

An annuity typically consists of payments that can occur annually, semi-annually, quarterly, or even monthly, making it a versatile instrument in financial planning and investment. The uniformity of the payment amount and the periodic nature of these payments are key characteristics that define an annuity.

In contrast, an annuity due refers specifically to payments made at the beginning of each period, while a perpetuity entails a series of payments that continue indefinitely, with no end date. A mortgage represents a different financial arrangement focused on real estate financing rather than a series of equal cash flows over time. Therefore, given the context of equal payments at equal intervals, "annuity" is the correct definition.