Step 1: A free particle in a plane has 2 position coordinates, \(x\) and \(y\).
Step 2: The constraint \(y = kx^{2}\) is a single holonomic equation relating them.
Step 3: Degrees of freedom \(=\) number of coordinates \(-\) number of independent constraints:
\[f = 2 - 1 = 1.\]
Step 4: Physically, once \(x\) is chosen, \(y\) is fixed by the curve, so a single generalized coordinate (e.g. \(x\)) describes the motion.
\[\boxed{f = 1}\]