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.
Deep, slow brain waves known as Delta Waves begin to emerge during this stage. It is a transitional period between light sleep and a very deep sleep. Stage Four. This is sometimes referred to as Delta Sleep because of the delta waves that occur during this time.Stage Four is a deep sleep that lasts for about 30 minutes. Sleepwalking and bed-wetting typically happen at the end of Stage Four sleep.ost dreaming occurs during Stage Five, known as REM. REM sleep is characterized by eye movement, increased respiration rate and increased brain activity. REM sleep is also referred to as paradoxical sleep because, while the brain and other body systems become more active, your muscles become more relaxed, or paralyzed.