Elementalism is both a philosophy and magic methodology, both centered around the theory that the six (?) elements are fundamental building blocks of the universe.
While magic traditions broadly have expanded beyond that – able to conjure things nominally outside of the elemental circle –, elementalist spellcasters staunchingly believe that everything in the universe is derived from those elemental powers. As such, they practice elemental magic as a means of discovering how to replicate all means and ways of other traditions via these limited tools and either discovering what elements they consist of, or whether they unwittingly used a then unknown element. I.e. Whether force spells are some mixture of air elementalism, or whether there is a yet uncovered force element driving them.