A butt plug is a sex toy. It’s a dildo especially made for anal penetration.
A butt plug is bulb-shaped: the middle is wider than the top or bottom.
When you insert a straight dildo in the anus and don’t keep it in place with your hands the muscles will force it out. But with a butt plug the sphincters of the anal opening will clench around the base, keeping it in place.
People who use butt plugs normally like the fullness they bring. Some like to put one in at the beginning of lovemaking and to leave it there through the course of lovemaking.

Using it safely