A more thorough explanation:

Definition: A vigilante is someone who takes the law into their own hands without having the legal authority to do so. They use force or the threat of force to enforce their own idea of justice. Vigilantes are different from people who simply report criminal behavior to the police.

Vigilantes are often motivated by a desire to seek revenge for a perceived harm or injustice. They believe that the legal system has failed to provide justice, so they take matters into their own hands.

• A group of citizens who patrol their neighborhood at night, looking for suspicious activity and confronting anyone they deem to be a threat.
• A man who sets up traps to catch thieves who have been stealing from his property.
• A woman who takes it upon herself to track down and confront her ex-boyfriend's new girlfriend, whom she believes is a threat to her safety.

These examples illustrate the definition of a vigilante because they all involve individuals taking the law into their own hands without having the legal authority to do so. They are motivated by a desire to seek justice or revenge, and they use force or the threat of force to achieve their goals. However, their actions are not sanctioned by the legal system, and they may be breaking the law themselves.