A gibbet is a structure that's used to execute criminals by hanging them. The execution of someone on a gibbet is an old-fashioned practice.
You can use the word gibbet to mean "gallows," or "public execution structure," and it can also be a verb, meaning to hang a person on one. Back in the days when executioners would routinely gibbet criminals in the public square, the bodies were often left on display — possibly to intimidate other potential criminals. The word gibbet has its root in the Old French gibet, "bent stick or gallows," from gibe, or "club."