What is mathematics?

Mathematics ("math") is the science of dealing with numbers, counting, and numerical

operations. It has several important branches dealing with actual or theoretical uses in

the physical world.

Math is the study of abstractions. Math allows us to isolate one or a few features such

as the number, shape or direction of some kind of object. Then we can study what can

be learned about the behavior of those features while ignoring everything else about

the object.

a subject in all schools.

It's the study of the theory and rules of numbers & their manipulations.

Algebra for example, apart from being the building-blocks of maths, (or "math" without the "s" in the US) is the rules of arithmetic in general form, hence its value in creating and manipulating formulae (specific equations to carry out particular tasks.

Mathematics underpins all the Sciences to varying degrees and in various ways, Engineering (the application of science to practical ends, not mending cars!), Administration and Business.

Without it you would not have the computer you're reading this on - you would not even have the electricity supply to which it's connected.

Without maths - or more accurately without the physics which works to highly mathematical rules - we would not exist. Nothing would!

So to say it's just a school exam subject is not an answer worthy of its author I'm afraid.