Diameter

Diameter, in Plane Geometry, is generally a straight line bisecting any system of parallel chords of a conic section. The lines which it bisects are termed its ordinates. In the circle, ellipse, and hyperbola, every diameter passes through the centre of the curve, and is there bisected; but it is only in the case of the circle that all diameters are equal. In the parabola, since the centre of the curve is at an infinite distance, all diameters are parallel to the axis.