perpetuity

(uncountable) The quality or state of being perpetual; endless duration; uninterrupted existence.

(countable) Something that is perpetual.

(countable, law) A limitation intended to be unalterable and of indefinite duration; a disposition of property which attempts to make it inalienable beyond certain limits fixed or conceived as being fixed by the general law.

(countable, finance) An annuity in which the periodic payments begin on a fixed date and continue indefinitely.