What is meant by "emergency stop"?

The term "emergency stop" refers specifically to an immediate halt of the train in response to an unexpected situation or hazard that requires prompt action to prevent accidents or injury. This could involve dangerous conditions on the tracks, signal malfunctions, or any other immediate threat that compromises safety. The key aspect of an emergency stop is its urgency and necessity; it is not a planned stop but rather a critical response to an unforeseen circumstance.

The other options do not describe an emergency stop accurately. A gradual reduction in speed indicates a controlled and planned deceleration, which does not align with the concept of an urgent response to danger. Stopping at a scheduled station is part of the normal operational routine and does not involve the urgency or immediate action that characterizes an emergency stop. With regards to a procedure for equipment testing, this involves specific protocols for assessing the functioning of equipment, rather than responding to an urgent safety situation.