Definition - What does Posse Comitatus mean?
Posse comitatus is a legal right bestowed upon county sheriff officers across the United States that allows them the ability to conscript any able-bodied person to help them in arresting someone else or otherwise bringing peace to a situation. It is considered to be the equivalent of law enforcement officers hiring the militia to assist them in carrying out the law.
If a sheriff creates a posse comitatus, then the appointment only lasts for the amount of time in which it takes to bring resolution to the current situation. The posse could theoretically be reappointed, but their powers are limited to the actions for which the sheriff asks for help.
Justipedia explains Posse Comitatus
The use of posse comitatus was more commonly seen back in the formation of the United States and in particular within the Wild West. Vigilante groups were commonly assembled to deal with situations that the standing sheriff could not deal with by himself.
In contemporary society, the United States is the only country that still employs the use of posse comitatus in law. It could be said that the Philippines is currently under a posse comitatus ruling by its president in hunting down drug dealers, but this right has not yet been signed into law there.