What does the Q signal “QRL?” mean?

The Q-signal "QRL?" translates to "Are you busy?" or, when asked on an open frequency, "Is this frequency in use?" It is a fundamental courtesy in amateur radio to send "QRL?" before initiating a CQ or a conversation to ensure you do not interfere with an ongoing QSO. If the frequency is indeed in use, another station will typically respond with "C," "Y," "YES," or "QRL" to indicate that they are busy and you should tune elsewhere. The distractors are incorrect because they refer to other operating practices. Full break-in operation is represented by "QSK," and listening for a specific station is indicated by the prosign "KN."