CQ

WordReference Random House Unabridged Dictionary of American English © 2026

CQ, 

1. Radio and Television a signal sent at the beginning of radiograms conveying general information or sent by an amateur as an invitation for any other amateur to reply.
2. Military charge of quarters.

Collins Concise English Dictionary © HarperCollins Publishers::

CQ noun

1. a symbol transmitted by an amateur radio operator requesting two-way communication with any other amateur radio operator listening