Cartes des Visites
"French for 'calling cards,' they were so named because they were the same size as a card one would leave when one called upon someone who wasn't home. It was an albumen print from a wet collodion negative, originally. Collecting these small cards became a popular activity on both sides of the Atlantic." From Photography: Archival Care and Management by Ritzenthaler and O'Conner, 2006.