A dildo is an object usually designed for sexual penetration of the vagina, mouth, or anus, and is usually solid and phallic in shape. Penis prosthetic aids, known as "extensions", are not considered dildos. 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. People of all genders and sexual orientations often use these devices for masturbation or for other sexual activity.