Under what circumstance is a Terry stop considered lawful?

A Terry stop is considered lawful when an officer has reasonable suspicion of criminal activity. This standard, established in the United States Supreme Court case Terry v. Ohio, allows law enforcement to temporarily detain an individual if the officer believes that the person may be involved in criminal activity based on specific and articulable facts. Reasonable suspicion is a lower threshold than probable cause, which requires a belief that a crime has been committed or is being committed.

In this context, having reasonable suspicion allows officers to conduct a brief investigative stop and, if necessary, a limited search (also known as a "frisk") for weapons to ensure their safety or the safety of others. It’s important that the officer can articulate the specific reasons for their suspicion; vague hunches are insufficient.

While probable cause and other situations may give rise to different forms of law enforcement action, they are not the basis for a Terry stop, which specifically relies on reasonable suspicion.