In radio communication and radio broadcasting, QSL is one of the Q codes used in radio communication. 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 are written confirmations of either a two-way radio communication between two amateur radio stations or a one-way reception of a signal from an AM radio, FM radio, or television station.
They can also confirm the reception of a two-way radio communication by a third party. A typical QSL card is the same size and made from the same material as a typical postcard, and many are sent through the mail as a standard postcard
I can remember in Elementary and Junior High School, as soon as I got home I'd run to the mailbox if Mom hadn't got the mail yet to see what wonders awaited me. These cards were amazing in the 1950's... Rare stamps from countries we could only see on a map!
I took this one to school to show friends
I was very happy to get this one in the mail
The concept of sending a post card to verify reception of a station (and later two-way contact between them) may have been independently invented several times. The earliest reference seems to be a card sent in 1916 from 8VX in Buffalo, New York to 3TQ in Philadelphia, Pennsylvania (in those days ITU prefixes were not used). The standardized card with callsign, frequency, date, etc. may have been developed in 1919 by C.D. Hoffman, 8UX, in Akron, Ohio. In Europe, W.E.F. "Bill" Corsham, 2UV, first used a QSL when operating from Harlesden, England in 1922.