Plain English Meaning
A warning that the autopilot has lost a working airspeed signal. Any autopilot function that needs to know the airplane's speed can no longer be trusted, and the pilot must take over those tasks manually.
Full Definition
An annunciation displayed by the autopilot or flight director system indicating that valid airspeed data is no longer being received from the air data computer or pitot-static system. When this fails, autopilot modes that depend on airspeed (such as IAS hold or speed-based pitch modes) become unreliable or are automatically disengaged.
Context Anchor
Seen on a flight display or autopilot-related when the ’s airspeed information becomes invalid or unavailable.