0Rotating (spinning) a two-dimensional figure about a line to produce a three-dimensional shape, called a solid of revolution.
 | A solid of revolution is a three-dimensional figure obtained by rotating a two-dimensional figure (or curve) around a straight line (called the axis) that lies in the same plane |
An example of a rotation about a line is the concept of a revolving door. The panel of one section of the glass door is "pushed" about a center pole, creating an outer cylindrical path around the pole. While the revolving door does not create a "solid", it does illustrate the process of revolution. If the door filled the entire space as it revolved, a cylindrical solid would be formed.
Let's start by rotating right triangle ACB about a vertical line, as shown below. As the triangle is revolved about the line, the vertices A and C remain stationary, while vertex B follows the path of a circle. As the triangle rotates, 
creates the outline of a cone. Since the triangle's interior is shaded, it creates the interior of the cone, creating a solid figure.
