Suppose we have an inequality $$y>x^2,$$ then obviously the answer is the part of the plane "enclosed" by the parabola.
However, is there any other way to define this part of plane besides "the answer of this inequality" as there are cases when it is not that simple (systems etc.)? If we can precisely define the interval on the number axis, then maybe there is a more formal way in this case? I guess it is possible to extrapolate the question for not only planes, but 3 and more dimensional spaces.
I possess regular highschool mathematics skills, I am just curious.