The ∫ is the ‘Integral’ symbol. It is typically seen as a rite of passage for those who know what it is, but it represents much more than years of calculus and differential equations or the area under the curve. The Integral symbol in math means:
A function of which a given function is the derivative, i.e., which yields that function when differentiated, and which may express the area under the curve of a graph of the function.
What!!!...lost you at derivative.
The better Definition is as follows: necessary to make a whole complete; essential or fundamental.