A seizure refers to the consequence of a sudden, uncontrolled discharge of neurons within the central nervous system, usually associated with a change in behaviour or awareness.
Epilepsy is a disorder characterised by transient but recurrent 
disturbances of brain function that may or may not be associated with impairment or loss of consciousness and abnormal movements or behaviour. Epilepsy is not a single disease, but may be a symptom of another disease e.g. epilepsy as a symptom of traumatic brain injury.