A flyaway is an uncontrolled departure of the drone — a situation where control has been lost and the failsafes fail to recover it. Typical causes are a control-link loss combined with a GNSS failure, a compass error, or radio interference that leaves the drone unable to hold position or return home.
The procedure is concrete: note the last known position and heading, try to re-establish the link, warn people nearby if needed, and report the occurrence. A flyaway is not just a lost drone — it is a safety event that can endanger other airspace users.