What is a chemical?

Answer 1

At its most basic level a chemical is something that will have a particular composition and a set of particular characteristics. You cannot change it or divide through physical means only through changing its actual chemical bonds.

For example, I cannot change the chemical composition of water by boiling or freezing it. It is still water just in a different physical state.

Answer 2

In the broadest sense a chemical is any substance consisting of matter. Now, go look up the definition of matter.