Any device which is inserted into or covers the mouth to muffle sound. A dominant may wish to gag his submissive during BDSM play because she's being too noisy or simply to increase her feelings of helplesness. You need to be careful with gags or things tied in the mouth because as well as restricting breathing, they can trigger a gag reflex and vomiting. Obviously that could turn out to be very nasty (and potentially lethal) if the submissive can't get the gag out so never leave someone alone when they are gagged. You might also want to think in advance about a substitute for a safeword. If the gagged person can't talk, how will they let you know if they're in trouble or want out?
Types of gags
Ball Gags: The most common are rubber ball gags which are soft and easy to bite. The ball is inserted in the mouth, and straps or string is attached to them to go around the head and be tied in back. So also have full head harnesses to keep the ball/bit in.
Japanese (wiffle) ball gag: These are seen in Japanese photos a lot, there are practice golf balls, usually white or blue. The whole make it a little easier to breath and drool.
O Ring: A gag with a large metal O ring that keeps the mouth spread open but makes it easy to breath. Some have attachments that can be inserted into them.
Also called the Overmouth Gag. A mostly cosmetic gag which covers the lower half of the face, from just below the nose down to the chin.
All about gags
The Quick Rope Bit Gag
Penis gag A plastic or rubber gag shaped like a penis that can be inserted in the mouth.
What is penis gag? Itís special mouth gag that usually have smaller penis on inside for submissive to suck on.You will see nothing but pure humiliation on submissive face while she/he drool unstoppable.
Kissing the gag that the captive is wearing. Though to outsiders this may seem odd, the sensation is very pleasurable for both partners.