A more thorough explanation:

Definition: The fellow-officer rule is a principle in criminal procedure that allows an investigative stop or an arrest to be considered valid even if the law enforcement officer lacks personal knowledge to establish reasonable suspicion or probable cause. This is as long as the officer is acting on the knowledge of another officer and the collective knowledge of the law enforcement office. It is also known as the Whiteley rule.

Example: Officer A receives a tip from a reliable informant that a suspect is carrying drugs in their car. Officer A relays this information to Officer B, who then stops the suspect's car and finds drugs in it. Even though Officer B did not have personal knowledge to establish probable cause, the stop and subsequent arrest are considered valid under the fellow-officer rule because Officer B was acting on the knowledge of Officer A and the collective knowledge of the law enforcement office.

The fellow-officer rule is important in allowing law enforcement officers to work together and share information to make arrests and protect the public. However, it is also important to ensure that the information being shared is reliable and accurate to prevent wrongful arrests and violations of individuals' rights.