Conic section

Conic section is called to the intersection of a right circular cone of two sheets with a plane that passes through its apex. They are classified into three types: ellipse, parabola and hyperbola.
The ellipse is the locus of points in the plane such that the sum of the distances to two fixed points called foci is constant. 

The hyperbola is the locus of the points of difference plane whose distances from two fixed points called foci, is constant and smaller than the distance between spots.
The parabola is the locus of points in the plane equidistant from a fixed point called the focus, and a line called the directrix.