A butt plug is quite simply a small toy that is inserted in the rectum. Once it's inserted, you can leave the butt plug in the rectum or move it in and out. Many people enjoy the sense of fullness that butt plugs bring, much in the same way many women enjoy the fullness experienced during vaginal sex. Others enjoy the sensation of inserting something in their anus.
Butt plugs come in all different shapes and sizes. For newcomers to the anal scene, the sizes sometimes appear ridiculous, but anal aficionados demand satisfaction and toy companies are more than happy to oblige. The smallest, (and most popular) butt plugs are less than an inch wide and about 3.5 inches long. The Love Plug exemplifies the classic design for anal stimulation, intended to be inserted anally and allowed to remain there through the course of lovemaking. Doc Johnson claims to have sold over 1 million of their small butt plug. From there, butt plugs increase in size to almost astronomical proportions.