Explain the meaning of these terms with reference to a concave mirror: radius of curvature, principal focus, and aperture.

The concave mirror is a spherical mirror whose reflection
surface is a section of an inner surface of a hollow
sphere.

The Centre of curvature of the concave mirror is
the centre of the sphere of which the concave mirror is a
part.

The centre of the reflecting surface of the concave
mirror is the pole of the concave
mirror.

Radius of curvature of
is the radius of the sphere whose section is the reflection surface of the concave
mirror.

The line through the centre of curvature and the
pole of the concave mirror is called the principal
axis.

The Principal
focus is a point on the principal axis through which if a ray is incident
on the mirror, then it gets reflected parallel to principal axis. All rays that are
incident parallel to principal axis gets reflected through principal axis. It lies
approximately half way between the centre of curvature  and the pole of the
mirror.

Aperture is the entire
area of the reflecting surface of the spherical mirror.