Answer:
Directrix
Step-by-step explanation:
The directrix of a parabola is the line, along with a point not on the line (which is the focus), which is used to generate a parabola. The directrix is parallel either to the x- or y-axis, and is perpedicular to the parabola's axis of symmetry (at x = h).
Therefore, the correct answer is "directrix."
