If an officer has a reasonable suspicion that a person is armed and dangerous, then the officer can conduct a frisk of that person for weapons. This frisk is a patting down of the exterior of the suspect and can be conducted to the extent to determine if the suspect is armed.
Legal Supplement
Terry v. Ohio, 392 U.S. 1 (1968),
[The frisk] must be confined in scope to an intrusion reasonable designed to discover guns, knives, clubs, or other hidden instruments for the assault of the police officer.
Sibron v. New York, 392 U.S. 40 (1968),
Before [the officer] places a hand on the person of a citizen in search of anything, he must have constitutionally adequate reasonable grounds for doing so. In the case of the self-protective search for weapons, he must be able to point to particular facts from which he reasonably inferred that the individual was armed and dangerous.
Ybarra v. Illinois, 444 U.S. 85 (1979),
[A] law enforcement officer, for his own protection and safety, may conduct a patdown to find weapons that he reasonably believes or suspects are then in the possession of the person he has accosted.
Nothing in Terry can be understood to allow a generalized cursory search for weapons or, indeed, any search whatever for anything but weapons.
Adams v. Williams, 407 U.S. 143 (1993),
The purpose of this limited search is not to discover evidence of crime, but to allow the officer to pursue his investigation without fear of violence, and thus the frisk for weapons must be equally necessary and reasonable.
