I.  The Parabola

    The parabola has one focus and one directrix.

    Locus Definition: 
    A parabola is the locus of points equidistant 
    from its focus and its directrix.


II. The Ellipse

    The ellipse has two foci and two directrices.

    Locus Definition:
    An ellipse is the set of points whose distance from the
    focus is equal to e times the distance to the
    directrix ( where 0 < e < 1).

III. The Hyperbola

    The hyperbola has two foci and two directrices.

    Locus Definition:
    An hyperbola is the set of points whose distance from 
    the focus is equal to e times the distance to the
    directrix ( where e > 1).