A seizure is a sudden burst of electrical activity in the brain that causes a temporary disturbance in the way brain cells communicate with each other.
The kind of seizure a person has depends on which part and how much of the brain is affected by the electrical disturbance that produces the seizure. A seizure may take many different forms, including a blank stare, uncontrolled movements, altered awareness, odd sensations, or convulsions. Seizures are typically brief and can last anywhere from a few seconds to a few minutes.
Seizures are divided into two main categories:

Generalised Seizure
Involve both hemispheres of the brain
Two common types are absence seizures (petit mal seizures) and tonic-clonic seizures (grand mal seizures)
Focal Seizures (Partial Seizures)
Only involve one part of the brain
Include focal impaired awareness seizures (complex partial seizures) and focal aware seizures (simple partial seizures)