If \(A = C\), then the answer is \(\boxed{\text{a circle}}\).
If \(A C = 0\), then the answer is \(\boxed{\text{a parabola}}\).
If \(A \neq C\) and \(A C > 0\), then the answer is \(\boxed{\text{an ellipse}}\).
If \(A C < 0\), then the answer is \(\boxed{\text{a hyperbola}}\).