Meaning of theta rhythm

the'ta rhythm"

Pronunciation: [key]
— Physiol. Physiol.
  1. a pattern of brain waves having a regular frequency of 4 to 7 cycles per second as recorded by an electroencephalograph, observed during various states of light sleep or arousal.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.