A very strong fire-based attack that hits all enemies and allies. 火炎流 / かえんりゅう [kaenryuu] or 'flowing flame' in Japanese. Note that many times, the summon Ifrit's signature attack was also translated as Inferno (some examples of it remain below), but that ability's actual translation is Hellfire.
Final Fantasy III
Target: all enemies, Element: Fire, Power: 220
Use: when casting Heatra on Summoner
Effect: deals a large amount of fire element damage on all enemies
Other: 地獄の火炎 [jigoku no kaen] or Hellfire in Japanese
Final Fantasy IV
MP required: 70 MP
Usable by: everyone (DS version only)
Obtain: find in Eblan Cave after the Rubicante fight
Final Fantasy XIV

Effect: 200 potency, Fire, cone aoe, additional Fire DoT with 20 pot
Cast time: instant, Cooldown: 300.0s
Range: 5 yalms, Radius: 5 yalms
Learn: SMN50, Use: Ifrit-Egi
Description: Deals fire damage with a potency of 200 to all enemies in a cone before it. Additional Effect: Fire damage over time with potency of 20 for 15s.
Other: is placed on a separate pet hotbar when usable
Other: 地獄の火炎 [jigoku no kaen] or Hellfire in Japanese
Airborne Brigade

SSR
Type: STR, Element: Fire-, Growth: Slow, Cost: 34
Attack: 12,200 (lv1), 38,917 (lv200), ? (lv220), 47,365 (lv240), ? (lv260), ? (lv280)
Defense: 12,300 (lv1), 38,642 (lv200), ? (lv220), 46,972 (lv240), ? (lv260), ? (lv280)
Obtain: event: Showdown ranking reward
Other: as 'Scorch'

Vaan I (SR summon)
Type: Legend, Element: -, Growth: Normal, Charge: 57
Brave: 2,547 (lv1), ? (lv240), ? (lv270), ? (lv300), ? (lv330), ? (lv360), ? (lv390), ? (lv420), ? (lv450), ? (lv480)
Ability: Inferno
Obtain: event: Showdown
Other: Note that this is note the same ability as most others on this page but instead based on the FF12 one. 炎のインフェルノ [honoo no inferno] or 'flame inferno' in Japanese
Record Keeper

Type: Soul Break, Rarity: -
Target: all enemies, Element: Fire/-, Gauge cost: 1 bar
Learn: Edge (equip Sasuke (VI))
Effect: Deals a strong fourfold long-range physical attack of Fire&Non elements without charge time on all enemies
Category: Ability