What shape is it without sides or corners?

Answer 1

As a 'shape' must be 2D at least (i.e. not a point or a line) then it must have sides (a circle having an infinite number) between each pair of adjacent sides there must therefore be an angle or it would be a line (again, not classically a shape)

Of course, if you DO allow lines and points to be classed as shapes, either one would fit the question.

There are also non-euclidean geometries where the rules can be very different.

:-)