ATC – Air Traffic Control.
For operations conducted in, or near, controlled airspace you may need to contact the ATC and often times have them issue a NOTAM for your UAV flights.
is a service provided by ground-based controllers who direct aircraft on the ground and through controlled airspace, and can provide advisory services to aircraft in non-controlled airspace. The primary purpose of ATC worldwide is to prevent collisions, organize and expedite the flow of traffic, and provide information and other support for pilots. In some countries, ATC plays a security or defensive role, or is operated by the military.