A more thorough explanation:

Gibbet law, also known as Halifax law, refers to an ancient form of private justice that was practiced in the parish of Halifax, England. It involved the summary and unauthorized trial and execution of a person accused of a crime, usually by decapitation. This punishment was carried out after a summary trial, without any legal process or evidence.

The term "gibbet law" comes from the forest of Hardwick, where the free burghers of Halifax used to practice this form of punishment against people accused of stealing. Thieves could be condemned to death by beheading on market day. The last known case of gibbet law occurred in 1650.

For example, if someone was accused of stealing a loaf of bread, they could be subjected to gibbet law without any legal process or evidence. This form of punishment was carried out by the free burghers of Halifax, who acted as judge, jury, and executioner. The accused person would be beheaded in public, as a warning to others.