Ictal refers to a physiologic state or event such as a seizure, stroke or headache. The word originates from the Latin ictus, meaning a blow or a stroke. In electroencephalography (EEG), the recording during an actual seizure is said to be "ictal".
Pre-ictal refers to the state immediately before the actual seizure, stroke, or headache, though it's recently come to light that some of characteristics of this stage (such as visual auras) are actually the beginnings of the ictal state.
Post-ictal refers to the state shortly after the event.
Inter-ictal refers to the period between seizures, or convulsions, that are characteristic of an epilepsy disorder. For most people with epilepsy, the inter-ictal state corresponds to more than 99% of their life. The inter-ictal period is often used by neurologists when diagnosing epilepsy since an EEG trace will often show small inter-ictal spiking and other abnormalities known by neurologists as subclinical seizures. Inter-ictal EEG discharges are those abnormal waveforms not associated with seizure symptoms.