The word perpetuity means "the property of lasting forever." The perpetuity of an eternal flame means that it will burn endlessly, while an ordinary candle flame will eventually extinguish.
Anything in perpetuity keeps on going and going and going. If you crash the family car and your parents ban you from driving it in perpetuity, you’re never driving that car again. First appearing in the 15th century, the noun perpetuity derives from the Latin word perpetuus meaning "continuing throughout."