A stuff gag is a gag that is, in fact, very rarely found on its own. Technically, a stuff gag consists of a piece of cloth stuffed into the subject's mouth. This extremely hampers tongue movement, and severely muffles throat movement (although it is a possible choking hazard). Although effective, a stuff gag on its own is easy to force out. Stuff gags are commonly coupled with other gags - usually tape gags or cleave gags. When coupled, the stuff gag becomes much more effective. Stuff gags are most commonly used in BDSM. For lighter purposes, a simple tape or cleave gag will suffice. In more intense scenarios, however, a stuff gag is often included, which minimizes the amount of noise a subject can make. It most notably minimizes throat sounds, which make even simple whining difficult. They are more effective in spanking scenarios, especially if the spanker wants to minimize noises from the spankee, such as whines or cries. Stuff gags are fairly simple to make, and are often comprised of handkerchiefs, pantyhose, or undergarments.
Using underwear as as a gag
In BDSM fiction and play, a person's nudity is especially emphasized when the same piece of underwear that used to cover their modesty until just moments ago is not only taken off, but then going into their mouth as a gag.