What is reasonable suspicion?

To conduct a Terry search, or a stop and frisk, police need reasonable suspicion that the person is suspected of imminent illegal behavior or past criminal activity. Reasonable suspicion is based on the totality of the circumstances as understood by those versed in the field of law enforcement; it is commonly described as something more than a hunch but less than probable cause. And what does totality of circumstances mean? It refers to an assessment based on all the circumstances, which includes objective observations, information from police reports, and consideration of the modes of patterns of operation of certain kinds of lawbreakers.