In the context of aviation and transportation, ATC stands for Air Traffic Control. This refers to the service provided by ground-based controllers who direct aircraft on the ground and through a given section of controlled airspace. Their primary mission is to prevent collisions, organize the flow of air traffic, and provide information and support for pilots. Controllers use tools like radar, high-frequency radio, and sophisticated computer systems to maintain "separation" between planes. In a different context, specifically in rail systems, ATC stands for Automatic Train Control, which is a suite of safety systems designed to monitor the speed of a train and automatically apply brakes if the driver fails to respond to signals or exceeds the speed limit. Both versions of ATC are fundamental to the safety of modern mass-transit and global travel systems.