Abnormality observed by electroencephalogram (EEG), which is used to record of the brain's spontaneous electrical activity from multiple electrodes placed on the scalp. The phenotype is EEG abnormality (HP_0002353, a Human Phenotype Ontology id). Also known as: Abnormal EEG, Abnormal electroencephalogram, EEG abnormalities, Electroencephalogram abnormal, Electroencephalogram abnormalities.