A seizure is a sudden surge of electrical activity in the brain. It usually affects how a person appears or acts for a short time.
These are not the same as an epileptic seizure, which is caused by a disturbance in the electrical activity of the brain.
NOTE: This is not the same as having epilepsy, which is a tendency to have seizures that start in the brain.
Generalised tonic clonic seizures (grand mal seizures) are the most common and best known type of generalized seizure.
Watch this video to see the first aid treatment for a generalised seizure
Source: Epilepsy Action
Important: Don’t try to keep the casualty still during the seizure or put anything in their mouth.

Focal and absence seizures look very different from a tonic clonic seizure a person having a focal seizure may not be aware of their surroundings or what they are doing.