One description of a parabola involves a point (the focus) and a line (the directrix). The focus does not lie on the directrix. The parabola is the locus of points in that plane that are equidistant from the directrix and the focus.
A parabola refers to an equation of a curve, such that a point on the curve is equidistant from a fixed point and a fixed line. Its general equation is of the form y^2 = 4ax (if it opens left/right) or of the form x^2 = 4ay (if it opens up/down)
A parabola is a curve where any point is at an equal distance from: Get a piece of paper, draw a straight line on it, then make a big dot for the focus (not on the line!). Now play around with some measurements until you have another dot that is exactly the same distance from the focus and the straight line.
Graphs of quadratic functions all have the same shape which we call "parabola." All parabolas have shared characteristics. For example, they are all symmetric about a line that passes through their vertex. This video covers this and other basic facts about parabolas.
In mathematical terms, a parabola can be defined as the locus of all points in a plane that are equidistant from a given fixed point (the focus) and a fixed line (the directrix).
Like the ellipse and hyperbola, the parabola can also be defined by a set of points in the coordinate plane. A parabola is the set of all points (x, y) in a plane that are the same distance from a fixed line, called the directrix, and a fixed point (the focus) not on the directrix.