Fire Pledge is one of the three moves that is taught by a man in Driftveil City in Pokemon White and Pokemon Black to Tepig, Pignite, Emboar, Chimchar, Monferno, Infernape, Torchic, Combusken, Blaziken, Cyndaquil, Quilava, Typhlosion, Charmander, Charmeleon, and Charizard. The move type is fire, and the damage is not as high as the move's counterpart - Blast Burn. This move was not available in games prior to the 5th Generation, and the move cannot be learned by any other means or be taught to any non-starter fire Pokemon or any other Pokemon besides the fire-type starters and/or their evolutions.
Using Fire Pledge in combination in battle with a Pokemon's use of Grass Pledge or Water Pledge will increase the power of Fire Pledge, and the effect will vary depending of the use of either of the two moves together.
Please note that when a Pokemon uses Fire Pledge while holding a Fire Gem, the damage and power of the move will be unaffected rather than boosted.