The second most common waveform occurring in electroencephalograms of the adult brain, characteristically having a frequency from 13 to 30 cycles per second. It is associated with an alert waking state but can also occur as a sign of anxiety or apprehension.
Any of the electrical waves from the parietal-frontal regions of the brain, having frequencies from 13 to 30 hertz: a sign of mental activity and alertness.
Webster's New World
An electrical oscillation occurring in the human brain at a frequency of about 13 to 30 hertz as recorded on an electroencephalogram, associated with a state of alert wakefulness.
American Heritage Medicine
(neurology) An electrical signal produced by the brain while the subject mentally active.