“Corner card” is a philatelic term meaning the imprinted return address, sometimes accompanied by a picture, that is found in the upper left corner of an envelope. Since corner cards are professionally printed, envelopes containing these imprints tend to be from commercial or institutional sources. However, envelopes with corner cards from private individuals are sometimes seen. While corner cards provide the sender’s return address to facilitate the return of undeliverable mail, they function in a similar manner to a business card or letterhead imprint, also advertising the sender’s business.
If you are aware of any corner cards that are not in the compilation, please let me know by reaching out to me through my contacts page.