What is the Q code that means "Who is calling me?" in amateur radio?

In amateur radio, the Q code "QRZ?" translates to "Who is calling me?" It is universally used by operators when they hear a transmission directed at them but cannot quite catch the full call sign. Operators frequently use this code after finishing a contact during a busy contest or pileup to invite the next station to identify themselves, or to ask a station that just transmitted to repeat their call sign. The other options serve completely different purposes. "QRM" refers to man-made interference, "QRP" means reducing transmitter power (or low-power operation), and "QRK" asks for the readability of the signal.