Definitions for "All Clear"
This was the British Civil Defence 'Raiders Passed' message, receipt of which would cause the sirens to sound a continuous signal for two minutes, indicating enemy aircraft had passed out of the area.
a signal (usually a siren) that danger is over
Signified by a siren at the end of a race, the all clear means that the stewards deem the finishing order of horses is correct and bets may be paid out. It also means that no protest or objection has been made by the connections of any horse in the race.
the verbal and visual instruction given by a field Umpire for the goal Umpire to signal and record a Goal or a Behind, as the case may be.
permission to proceed because obstacles have been removed