Reality is a set of axiomatic statements that can be interpreted as "rules" or "laws." All other existences (matter, energy, thought, etc) are particulars. All particulars operate under the constraints of Reality.
Reality isn't a thing; It's a statement.
Nothing has a definition, just words created to have an idea of "definitions" what if we are unreal? What make us more real than a dream? Blah blah blah.