*Runs towards you*
"Hi Senpai, i assume you want me to tell you what fire is in life and narutoverse.
*Takes a deep breath*
Fire is a raw and both destructive yet productive element. They are a source of energy and are used for both lighting and heating, without certain fires eg the sun,(its a flaming gas ball if you really wanna get technical ) Life on earth would eventually become a extreme, void of most life due to the massive drop in tempreture.
Fire is also a destructive force that can occur naturally or easily be produced by man. In nature flames are usually produced by the suns rays concentrating to much on a specific spot that is parched and void of most water such as hay, or created by the extreme heat given off from lightning strikes and the ground to which the lightning strike connects to being dry.
Forest Fires are caused very often by one of the two previous reasons although it seems that the forest fire would be a complete negative to the land in which it happens, it can sometimes have positive effects such as spreading the seeds of certain plants allowing even more plants and trees to grow next time around, the smoke of the wildfire will also speed up the plant seed's germination progress.
In Narutoverse Fire is weak to water yet strong to wind. Water stifles the growth of the flames and eventually puts it out,while wind acts as a sort of fuel making the flames grow stronger and larger.
Fire is a strange element in that unlike the other elements such as Earth or water it is not a solid or a liquid,but it is more closer to a Gas but not quite.
A example of a fire justu is Great fire ball
A example of a Fire release user in the manga is Jiriya
There are quite a Few Bloodlines that are created by combining fire with another element(s) such as Lava Release, Boil Release,Blaze Release or Steel Release