What is strap-on dildo?

Here is some information from wikipedia about strap-on dildos.

A strap-on dildo (also strap-on, dildo harness) is a dildo designed to be worn (usually in a harness) by one partner and used to penetrate another partner vaginally, anally or orally, used by both heterosexual and homosexual couples.

For a woman, a strap-on can be used to anally penetrate a man (pegging), or used vaginally, anally, or orally for lesbian intercourse.

For a man, a strap-on can be worn for penetrative sex, and may be used in cases of erectile dysfunction, for double penetration, or to penetrate multiple partners. A wide variety of harnesses and dildos are available, with different ways of fitting the wearer, attaching the dildos, stimulating the wearer or the receiver, and all with different features, advantages, and drawbacks for both users.