any of the electrical waves from the parietal and occipital regions of the brain, having frequencies from 8 to 13 hertz: a sign of relaxation, since they indicate a lack of sensory stimulation in a conscious person
See alpha wave in American Heritage Dictionary 4
A pattern of smooth, regular electrical oscillations in the human brain that occur when a person is awake and relaxed. As recorded by the electroencephalograph, alpha waves have a frequency of 8 to 13 hertz. Also called alpha rhythm.