This article appears to be a dictionary definition.
Ictal period refers to a physiologic state or event such as a seizure, stroke, or headache. The word originates from the Latin word ictus, meaning a blow or a stroke. In electroencephalography (EEG), the recording during a seizure is said to be "ictal". The following definitions refer to the temporal relation with seizures.
Pre-ictal refers to the state immediately before the actual seizure, stroke, or headache.
Post-ictal refers to the state shortly after the event.
Interictal refers to the period between seizures, or convulsions, that are characteristic of an epilepsy disorder. For most people with epilepsy, the interictal state corresponds to more than 99% of their life. The interictal period is often used by neurologists when diagnosing epilepsy since an EEG trace will often show small interictal spiking and other abnormalities known by neurologists as subclinical seizures. Interictal EEG discharges are those abnormal waveforms not associated with seizure symptoms.
Peri-ictal encompasses pre-ictal, ictal and post-ictal.