The individual cards may or may not have been printed at the same time. Examples are Sunbonnets, Bonzo, and Mickey Mouse. More than just a common topic, a series has a common artist and publisher. Postcards published in a group of four, six, seven, eight, or twelve. These were sold in packets or individually.
Examples are days of the week or months of the year.
Silk Postcards where silk fabric is applied to the design, or the total image is printed on silk fabric, then attached to a postcard back. See Woven in Silk. An optical instrument with two lenses, through which photographs taken in pairs from slightly different angles appear to have solidarity and relief. Top T Topics Postcards that are not views, but are of subjects such as baseball, kites, cats, and golf. Tradecards Advertising cards issued before 1900.