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.
Different types of butt plugs
Santa Claus on the Eendrachtsplein, Rotterdam
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 about the average length of an erect penis, 4–6 inches (10–15 cm), but some may be longer. A dildo's circumference is typically 4–5 inches (10–13 cm).
Two women embracing and using carrots as dildoes, 19th century India.
Acrylic dildo shaped like a torpedo
A woman with a dildo. Red figure amphora attributed to the Flying-Angel Painter c. 490 BC; City of Paris Museum of Fine Arts
Dildo being used by two women. Lithograph from De Figuris Veneris (1906) by Édouard-Henri Avril