Chambers 20th Century Dictionary(0.00 / 0 votes)Rate this definition: Sibilance. sibâ²i-lans, n. a hissing soundâalso Sibâ²ilancy.âadj. Sibâ²ilant, making a hissing sound.ân. a sibilant letter, as s and z.âv.t. Sibâ²ilÄte, to pronounce with a hissing sound.ân. SibilÄâ²tion, a hissing sound.âadjs.
Definition: A delta wave is a type of high amplitude brain wave found in humans. Delta waves have a frequency from one to four hertz and are measured using an electroencephalogram (EEG). These brain waves are thought to emerge from the thalamus and are generally associated with slow-wave sleep (during stages three and four of the stages of sleep.
1 Delta waves (below 4 hz) occur during sleep. 2  Theta waves (4-7 hz) are associated with sleep, deep relaxation (like hypnotic relaxation), and visualization. 3  Alpha waves (8-13 hz) occur when we are relaxed and calm. 4  Gamma brain waves (39-100 hz) are involved in higher mental activity and consolidation of information.