Definition
ATC SECURITY SERVICES POSITION
The position responsible for providing ATC security services as defined. This position does not provide ATC, IFR separation, or VFR flight following services, but is responsible for providing security services in an area comprising airspace assigned to one or more ATC operating sectors. This position may be combined with control positions.
Source: FAA Pilot/Controller Glossary (verbatim from the Federal Aviation Regulations).