Failsafe is the drone's pre-programmed behaviour for the moment something fails — most commonly after losing the control link or the GNSS signal. Typical options are hovering in place, landing straight down, or an automatic return to the home point.
The remote pilot must know which failsafe is configured on their drone and check it during the pre-flight inspection. This behaviour is part of the emergency procedures the pilot is personally responsible for — the wrong setting at the moment of link loss can turn a glitch into a crash.