Young woman wearing EEG cap (source)
An EEG is an electroencephalogram, a test that records electrical activity of the brain through wires attached to the scalp. Seizures are caused by abnormal electrical activity, which can often be identified by the EEG. Different patterns suggest different disorders, and should be read by a neurologist.
Seizures do not indicate any one specific neurologic disorder; they are seen in many people with developmental delays, in people with no learning delays, and in autistic people.
About 30-40% of autistic people develop seizures during their lifetimes. Two or more seizures that are not caused by fever or something like low blood sugar results in a diagnosis of epilepsy, which also may be called a "seizure disorder."
All people with nonfebrile seizures or complicated febrile seizures (one that lasts a long time or is associated with paralysis) should see a neurologist and have an EEG done. Template:Wikipedia