Repetitive waveforms may repeat in quick succession (rhythmic) , after nearly regular intervals (periodic), or spike and wave (SW). Periodic discharges are considered markers for neuronal injury. Most forms of repetitive abnormalities are epileptogenic; in specific situations they may also represent ictal patterns. GSW discharges of more than 3 Hz or other evolving discharges of more than 4 Hz are unequivocally ictal patterns, whereas GSW of less than 3 Hz or other evolving discharges of less than 4 Hz lie on an ictal-interictal spectrum. This means that these patterns may or may not be ictal depending on their clinical and electrographic accompaniments. A repetitive pattern is described as a combination of a main term 1 with a main term 2 based on the American Clinical Neurophysiology Society (ACNS) standardized critical care EEG terminology. Main term 1 could be either generalized (G), lateralized (L), bilateral independent (BI), or multifocal (Mf). Main term 2 could be either periodic discharges (PD), rhythmic delta activity (RDA), or generalized spike-wave (GSW). Common rhythmic abnormalities include GRDA and LRDA. Common periodic abnormalities include GPDs, LPDs, and BIPDs.The term “SI” is added to the combination of main terms to denote a stimulus-induced pattern (e.g., SI-GPDs for stimulus-induced GPDs).