ADS-B or Automatic Dependent Surveillance Broadcast is part of the FAA's NextGen National Airspace System. The FAA has begun to move away from ground radar systems and towards satellite-based GPS technology.
Starting January 1st, 2020, you must be equipped with at least ADS-B Out in order to fly in most controlled airspace. Federal Regulations 14 CFR 91.225 and 14 CFR 91.227 contain the details. Learn More.