Perpetuity is another way of saying "Forever".
1. The condition of an estate that is limited so as to be inalienable either perpetually or longer than the period determined by law.
2. An estate so limited.
Duhaime Legal Dictionary
Forever; of unlimited duration.
The condition of a future estate limited in such a way as not to vest within the period fixed by law for the vesting of an estate
A perpetuity is an annuity that has no definite end, or a stream of cash payments that continues forever. There are few actual perpetuities in existence (the United Kingdom (UK) government has issued them in the past; these are known and still trade as consols). A number of types of investments are effectively perpetuities, such as real estate and preferred stock, and techniques for valuing a perpetuity can be applied to establish price. Perpetuities are but one of the time value of money methods for valuing financial assets.