Epilepsy is more properly known as "the epilepsies", as there are dozens of different seizure disorders and syndromes in the international classification. Most basically, however, epilepsies are classified into either generalized or partial seizures. Partial seizures begin in one place in the brain, called the seizure focus, and affect only part of the brain.
These epilepsies are then sub-classified as:
Epilepsy of an unknown origin. In many cases it is presumed to be genetic.
When the cause of a person's epilepsy is identifiable. Basically, any lesion, scar, tangle of blood vessels or any other abnormality in the brain that can interfere with its delicate electrical workings can cause epilepsy. Common causes are head injury (ex. from a car accident); brain tumor, scar or lesion; brain injury during fetal development; birth trauma (ex. lack of oxygen during labor); aftermath of infectious diseases (ex. meningitis, encephalitis, measles); poisoning from substance abuse, like alcohol; and stroke.
If epilepsy is due to an acquired brain lesion which has not been identified, or the cause of which is unknown, its cause is hidden.