noun

• (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.