Ordinate
in analytical geometry, the ordinate of a point is one of the elements of reference, by means of which the position of a point is determined with respect to fixed straight lines, taken as co-ordinate axes. The ordinate of a point to a diameter of a conic section is the distance of the point from that diameter, measured on a line parallel to a tangent drawn at the vertex of the diameter.
The ordinate to a diameter is equal to half the chord through the point which is bisected by the diameter.