QSL is one of the Q codes used in radiocommunication and radio broadcasting. 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". A QSL card is a written confirmation.

QSL cards confirm either a two-way radiocommunication between two amateur radio stations or a one-way reception of a signal from an AM radio, FM radio, television or shortwave broadcasting station. They can also confirm the reception of a two-way radiocommunication by a third party listener. A typical QSL card is the same size and made from the same material as a typical postcard, and most are sent through the mail as such.