Question

why concave and convex mirror are called spherical mirror?

Answer 1

They are called spherical mirrors because their surfaces are not plain.

Answer 2

Because they’re a part of spherical mirrors.

If you cut a small part spherical mirror you will get concave or convex mirror depending on the painted surface.

They’re made in such a manner that all the perpendicular lines drawn from curved surface meet at a single point (radius of curvature).