Epilepsy and a seizure do not always mean the same thing. In other words, not every seizure means epilepsy!
A seizure is a sensory, motor or behavioural disturbance, or a corresponding change recorded on an EEG, resulting from abnormally excessive, paroxysmal and synchronised firing of neurons in the cerebral cortex. Some people may have a seizure only once in their life due to various external provoking factors. External provoking factors include intoxication, injuries, heatstroke, sleep deprivation and so on.
Epilepsy, however, is characterised by recurrent seizures that are not provoked by external causes. A provoked seizure may well not mean the disease epilepsy. Also, during loss of consciousness related to epilepsy, patients do not squeeze their eyes tightly shut. An epileptic syndrome is the combination of symptoms and signs of seizures that consistently occur together and in the same pattern.