Bottom line: Ataxia refers to incoordination or clumsiness of movement not associated with muscle weakness. Cerebellar ataxia is associated with incoordination of voluntary movements, displayed as delayed onset, jerky movement, dysmetria (ie, misjudging the target by overshooting or undershooting on finger-nose-finger test) , or intention tremor (side to side tremor on approaching the target of finger-nose-finger test.)
For more details: Disorders of equilibrium: Ataxia. In: Clinical Neurology, 7th ed. [AccessMedicine].
Coordination and cerebellar testing. In: Evidence-based Phyical Diagnosis, 2nd ed. St. Louis: Saunders Elsevier, 2007. p. 793-4. (Available at EUH Branch Library)