Smoke Release (煙遁, Enton) is one of the two kekkei genkai common amongst the Nagakura clan of Kirigakure. The natures comprising the ash release style are fire and wind. With it the user is capable of producing smoke within their bodies and then expelling it through their mouth, nostrils or even their pores.
According to Rosuto Nagakura the use of Smoke Release dates back to the clans early formation. Those who formed the Nagakura line could, on at least some scale, utilize smoke amongst their jutsu and create it within their bodies without suffering adverse reactions. Their techniques also couldn't be replicated through use of the Sharingan. It was this -- coupled with the similar Ash Release -- that made others covet the ability.