a kind of curve; one of the conic sections formed by the intersection of the surface of a cone with a plane parallel to one of its sides. it is a curve, any point of which is equally distant from a fixed point, called the focus, and a fixed straight line, called the directrix. see focus.-one of a group of curves defined by the equation y = axn where n is a positive whole number or a positive fraction. for the cubical parabola n = 3; for the semicubical parabola n = /. see under cubical, and semicubical. the parabolas have infinite branches, but no rectilineal asymptotes.