What does the code "QSB" mean in amateur radio?

QSB is the standard Q code used to report that a received signal is fading in and out. This phenomenon is very common in High Frequency (HF) communications due to changing atmospheric and ionospheric conditions. The distractors represent other situations: "I am busy" is QRL, "I am confirming contact" is QSL, and "I have no message" is QRU. A popular mnemonic for QSB is "Signal Bouncing" or "Signal Breaking", which accurately describes the fading nature of the transmission.