What does a large letter "X" near the runway threshold indicate?

The presence of a large letter "X" near the runway threshold signifies that the runway is closed. This visual indication is crucial for pilots as it clearly communicates that the runway should not be used for takeoff or landing. The "X" marking is an internationally recognized signal alerting all aviators to the closure, thereby ensuring safety and preventing potential accidents.

In aviation, different markings and signals are used to convey specific information about airport and runway status, and the large "X" is specifically designated for denoting that a runway is not in service.