What is "vertex of a surface of revolution"

Vertex \Ver"tex\, n.; pl. Vertexes, L. Vertices. [L. vertex, -icis, a whirl, top of the head, top, summit, from vertere to turn. See Verse, and cf. Vortex.] A turning point; the principal or highest point; top; summit; crown; apex. Specifically:

1. (Anat.) The top, or crown, of the head.

2. (Anat.) The zenith, or the point of the heavens directly overhead.

3. (Math.) The point in any figure opposite to, and farthest from, the base; the terminating point of some particular line or lines in a figure or a curve; the top, or the point opposite the base.

   Note: The principal vertex of a conic section is, in the parabola, the vertex of the axis of the curve: in the ellipse, either extremity of either axis, but usually the left-hand vertex of the transverse axis; in the hyperbola, either vertex, but usually the right-hand vertex of the transverse axis.

   Vertex of a curve (Math.), the point in which the axis of the curve intersects it.

   Vertex of an angle (Math.), the point in which the sides of the angle meet.

   Vertex of a solid, or Vertex of a surface of revolution (Math.), the point in which the axis pierces the surface.