What is the directrix of a parabola?

A parabola is the set of all points equidistant from a point (called the "focus") and a line (called the "directrix"). See this video to learn more about this. read more

A parabola is defined as follows: For a given point, called the focus, and a given line not through the focus, called the directrix, a parabola is the locus of points such that the distance to the focus equals the distance to the directrix. read more

A parabola is a locus of points equidistant from a single point, called the focus of the parabola, and a line, called the directrix of the parabola. It's easiest to understand this concept by examining the pictures below. read more