QSL card

A QSL card is sent to confirm radio communication, today, usually by amateur shortwave/ham radio operators. QSL is code for "I confirm receipt of your transmission". In the past, they were also sent to acknowledge signal reception of commercial broadcast stations.

The cards are postcard size allowing them to be mailed. QSL cards typically include the operator's call sign and other data, and can be plain but often are printed in a decorative style. Thus, the cards make an interesting collection aside from being a contact record. Today, the confirmation can just be a message sent via the internet.