A suppository is a semi-solid medication (typically in a bullet or torpedo shape) that is inserted into the rectum (rectal suppository), vagina (vaginal suppository) or urethra (urethral suppository). Once inserted, it slowly dissolves by the body's temperature, releasing the active drug.
The finger that pushes the suppository in should have short-trimmed fingernail, or a medical glove should be worn so that the anus will not be injured. Scientists found out in 1991 that rectal suppositories are best inserted (somewhat counter-intuitively) with the blunt end first and the pointy end last, which lets the suppository slip inside better.
Suppositories are sometimes given to adult babies and adult children. Suppositories as forms of "anal punishment" (mainly for their humiliating effect) are also featured on some spanking sites such as Kara Prepare Yourself.