Lava Release (溶遁; 熔遁, Yōton, English TV: "Corrosion Style" or "Lava Style") is a nature transformationkekkei genkai, a combination of fire and earth. Whereas most kekkei genkai are largely identical between users, Lava Release has a variety of forms depending on who's using it.
There is a subtle difference in the meaning of the kanji used for this kekkei genkai. Although both mean "to melt", the kanji with the "fire" (火) radical (熔) is outdated and means "melting with fire", whereas nowadays the kanji with the "water" (水) radical (溶) is normally used. Mei Terumī's Lava Release: Melting Apparition Technique, which utilises a strong acidic fluid, is the only Lava Release technique written with 溶. This, along with Jin no Sho stating that Mei's Lava Release kekkei genkai can only be used by her, indicates a difference between 溶遁 and 熔遁.
In Sha no Sho, the "water" kanji is used in Rōshi's entry, whereas in the glossary, the "fire" kanji is used. In Jin no Sho, only the "fire" kanji is used for Rōshi's Lava Release.