Real photo postcardとは 意味・読み方・使い方

In 1903 Kodak introduced the No. 3A Folding Pocket Kodak. The camera, designed for postcard-size film, allowed the general public to take photographs and have them printed on postcard backs. They are usually the same size as standard vintage postcards (3-1/2" x 5-1/2"). Also known by the acronym "RPPC".
Kodak's 3A camera pioneered in its use of postcard-size film but was not the only one to make Real Photo postcards. Many other cameras were used, some of which used old-fashioned glass plates that required cropping the image to fit the postcard format.