Directrix

A directrix is a fixed straight line used as a reference point when defining a parabola. For any point on the parabola, the distance to the focus (a specific point) is always the same as the distance to the directrix. This constant relationship helps in precisely defining and drawing the parabola, highlighting its geometric properties. Think of the directrix as a baseline that, together with the focus, helps shape and position the parabola in space.