I can fill in the blank by just listing the different fields of maths but my goal is to define all of mathematics.
An answer that I would've accepted a few years ago is "Maths is the study of numbers." But certain fields like topology and game theory do not have much to do with numbers.
A mathematician proposed "Mathematics is the study of the meaning behind numbers" but again that's assuming there can't be maths without numbers.
Another: "Maths is the study of abstraction" but that's just … abstract.
So what is maths?