Description and uses General A dildo is a device usually designed for penetration of the vagina , mouth, or anus , and is usually solid and phallic in shape. Some expand this definition to include vibrators. Others exclude penis prosthetic aids, which are known as "extensions". Some include penis-shaped items clearly designed for vaginal penetration , even if they are not true approximations of a penis. Some people include devices designed for anal penetration butt plugs , while others do not.