Ardupilot supports many kinds of object avoidance in vehicles. Airborne Vehicles (ADSB), Object Avoidance (Object/Ground/Ceiling), and Geo-Fences (Beacons, Exclusion zones, Fences). Supported types vary with vehicle. Some kinds of avoidance require external hardware, such as ADSB receivers or Rangefinders.
Various strategies are employed and vary depending on vehicle, mode, and/or object to be avoided. Re-routing, slide, stop, or failsafe style actions are the most common ones. See the particular Avoidance Feature below for details.