From Final Fantasy Wiki

Ardor (アーダー, Ādā), spelled Ardour in the PAL version of the game, is a Black Magick spell exclusive to Final Fantasy XII. Regarded as the most powerful Fire-elemental spell that targets all enemies, Ardor can be bought from the Bangaa in Barheim Passage, after the Pharos at Ridorana is completed. It costs 15,600 gil and 60 License Points. This is, most likely, the player version of Firaja. Its appearance is unique for a Fire spell as the flames created upon casting are blue instead of the normal red, yellow, or orange; this is to show its increased intensity as blue flames are hotter than red ones.

In the International Zodiac Job System version, Ardor has been moved into the Arcane Magick category and can only be used by Red Mages. It is a Level 3 Magick and costs 110 LP. It is not available in shops, but can be found in a chest at the Pharos at Ridorana, specifically the Third Ascent/Spire Ravel - 2nd Flight, hidden area north-east.