A butt plug is a sex toy that is designed to be inserted into the rectum for sexual pleasure. They are similar to a dildo in some ways but tend to be shorter and have a flanged end to prevent the device from being lost inside the rectum.
A dildo is a sex toy, often explicitly phallic in appearance, intended for sexual penetration or other sexual activity during masturbation or with sex partners. Dildos can be made from a number of materials and shaped like an erect human penis. They are typically 4–6-inch (10–15 cm) in length, about the average length of an erect penis, but some may be longer, and circumference is typically 4–5-inch (10–13 cm).