Butt plugs (or anal plugs) are sex toys designed to be inserted in the anus and rectum for sexual pleasure. In some ways, they are similar to a dildo, but they tend to be shorter, and to have a flared end to prevent the device from being lost inside the rectum. (It is generally ill-advised to use a standard dildo anally, since it may get stuck, requiring medical extraction.)
The users of butt plugs include men and women of all sexual orientations.