The "fire element" has many varied meanings, depending on which philosophical, religious or cultural thought it is applied to. Several explanations of the phrase are given in the Wikipedia entry for "Fire (classical element)", which can be found below.

It is in classical mythology, but not in reality. In reality fire is not even a substance but a chemical reaction between oxygen and some flammable substance.

which key element contained in the Baroque music that classical music left out

The Fire Chakra element allows you to use Fire Element Jutsus.. Like the Fireball Jutsu..

the return to "classical" thought