A quadratic function is a real function f such that f(x) = ax² + bx + c for all x in ℝ, where a, b and c are real numbers, with a ≠ 0. The graph y = f(x) of such a function is a parabola with its axis parallel to the y-axis, and with its vertex downwards if a>0 and upwards if a<0. The term equally applies to degree two polynomials over other fields and rings.