In aviation, what does "squawk" mean?

In aviation, "squawk" specifically refers to the action of setting the aircraft's transponder to a specific code. This code is assigned by air traffic control and is used for identification and tracking purposes on radar. When a pilot is instructed to "squawk" a certain code, it allows air traffic controllers to differentiate the aircraft from others in the airspace. This process enhances situational awareness and improves flight safety by enabling ATC to monitor the aircraft's position and altitude effectively.

The other concepts presented in the options are related to aviation but do not pertain to the term "squawk." Checking engine performance involves monitoring the aircraft's powerplant, requesting altitude changes is a communication action with air traffic control, and reporting malfunctioning instruments deals with addressing issues within the cockpit systems. However, none of these actions align with the specific definition of "squawk" in the context of transponder usage.