Snoring is the fluttering noise due to partial obstruction of the upper airway, when the muscles at the back of the throat relax during sleep.
Most of the noise comes from the Soft palate. In the case of mild snorers, there is often increased floppiness, and more fluttering regions. In severe cases, complete obstruction (breath-holding) may occur intermittently during sleep. This is known as Obstructive Sleep Apnoea (pronounced: ap-knee-uh), which can be a major health concern.