An eternal flame is a flame, lamp or torch that burns for an indefinite time. Most eternal flames are ignited and tended intentionally, but some are natural phenomena caused by natural gas leaks, peat fires and coal seam fires, all of which can be initially ignited by lightning, piezoelectricity or human activity, some of which have burned for hundreds or thousands of years.

Atar, Atash, Azar or Dāštāɣni, is the Zoroastrian concept of holy fire, sometimes described in abstract terms as "burning and unburning fire" or "visible and invisible fire". It is considered to be the visible presence of Ahura Mazda and his Asha through the eponymous Yazata. The rituals for purifying a fire are performed 1,128 times a year.