A more thorough explanation:

Posse comitatus is a Latin phrase that means "the power of the county." It refers to a group of citizens who are called upon to assist a sheriff in keeping the peace, conducting a rescue, or apprehending a criminal.

The extent of powers that a sheriff can delegate to a posse varies depending on the jurisdiction. In California, for example, any person who assists a police officer in law enforcement activities and is not an independent contractor is considered to be a public employee and is entitled to compensation for their efforts.

If a person in a posse comitatus is injured or killed while performing the requested law enforcement activity, they are to be indemnified at a rate of up to four times his or her average annual earnings, inclusive of any posse comitatus compensation.

At the discretion of a sheriff, as many people as deemed necessary to assist in law enforcement may potentially be recruited, subject to no limitations. Most recently, SB-192 decriminalized the refusal to participate in a posse comitatus, which formerly was a misdemeanor and carried an accompanying fine.

For example, a sheriff may call upon a posse comitatus to help search for a missing person in a remote area. The posse members would assist in the search and provide any necessary support to the sheriff's department.

Another example would be a posse comitatus being called upon to help maintain order during a large public event, such as a protest or parade. The posse members would assist law enforcement in keeping the peace and ensuring the safety of all involved.