Confirmation Of Reception
to acknowledge receipt. Commonly used to indicate "I understand", "I coped your transmission (or report) all OK". Also used as a term for sending cards by mail to confirm a two way contact with a station, such as QSL via the bureau. (see bureau or burro).
In radiocommunication and radio broadcasting, QSL is one of the Q codes used in radiocommunication. A Q code message can stand for a statement or a question. In this case, QSL means either 'do you confirm receipt of my transmission' or 'I confirm receipt of your transmission'.