This is the MDE Glossary (copied from: www.yourdictionary.com).

directrix

A fixed curve traversed by a generatrix in generating a conic section or a cylinder.

eccentricity

The ratio of the distance of any point on a conic section from a focus to its distance from the corresponding directrix. This ratio is constant for any particular conic section.

focus/foci

A fixed point whose relationship with a directrix determines a conic section.

Slope

The rate at which an ordinate of a point of a line on a coordinate plane changes with respect to a change in the abscissa.
The tangent of the angle of inclination of a line, or the slope of the tangent line for a curve or surface.