What does "squawking" indicate in aviation?

In aviation, "squawking" primarily refers to the action of setting the aircraft's transponder to a specific code that communicates with Air Traffic Control (ATC). When an aircraft squawks a certain code, it allows ATC to identify the aircraft on their radar systems, along with its altitude and other information depending on the features of the transponder. This is crucial for maintaining safety and situational awareness in busy airspace, as it helps ATC manage multiple aircraft and prevent collisions.

The relevance of the other options can be noted where recording flight details on a strip is part of the documentation process, which does not involve the transponder. Reporting flight delays pertains to communication between pilots and ground control about schedule changes or issues impacting timing, and acknowledging a control instruction refers to the pilot confirming directives from ATC but does not involve the transponder. Thus, the action of "squawking" is a specific and technical term directed towards transponder usage, making setting the aircraft's transponder code the accurate interpretation.