Fire is one of the 7 elemental damage types.
Fire is the racial damage type of the Fyros. The fire damage elemental spell can only be learned from a Fyros magic trainer once a mage reaches level 125 elemental magic. It is generally the preferred damage type to use while in the desert, as creatures there tend to resist it poorly.
Most animals and most intelligent plants have no protection against Fire magic; exceptions are the Rendor, Tyrancha, Varinx, and Shooki. Most kitin do have protection against Fire magic, though in the case of Kincher, Kirosta and Kinrey it's no more than against any other elemental damage type. Outpost guards in desert outposts are immune to Fire spells.
Protection from Fire
Fyros player characters have a natural 20% protection from Fire damage. Any player can protect themself against Fire damage by wearing jewelry that gives additional Fire protection. You can have at maximum 70% protection, whether you're Fyros or not.
You can also increase your chances of resisting a Fire elemental spell by wearing jewelry that raises your Desert resistance.
Non-magical Fire damage
Kipesta have a natural flamethrower which does Fire damage, but this attack itself is physical and not magical in nature. That means Fire protection will protect you against it, but Desert resistance will not help you resist it.
Many bandits and tribes guards also have random elemental damage added to their melee and ranged attacks, including Fire. If you're hit with Fire damage that way, Fire protection will decrease that damage, but Desert resistance will not help you resist it.