What type of message might include a "stop and wait" instruction?

A "stop and wait" instruction is typically associated with communication that requires immediate attention and could potentially affect safety or operations, such as changes in signals or track work. In these situations, the urgency of the instruction necessitates that the receiving crew stop their current actions and await further updates or information before proceeding. This is crucial to ensure safe operation, as any misunderstandings or lack of attention to such messages could lead to dangerous situations.

On the other hand, routine check-in messages, confirmations of arrival at a station, or maintenance update requests often involve standard communication where immediate halting of operations isn't crucial. These types of messages do not usually require the same level of urgency that would warrant a "stop and wait" directive.