Diameter
in geometry, a line drawn passing through the center of a circle or other curvilinear figure, and terminating each way in the circumference. That point which bisects all lines drawn through a figure from side to side is called a center, and every line drawn through a center and terminating in the circumference or opposite boundaries is a diameter. Every circle has an infinite number of diameters. A diameter which is perpendicular to the chords which it bisects is called an axis. A circle has an infinite number of axis, every diameter being an axis. The parabola has one axis and each of the other conic sections two axes.