A postal card is a typically rectangular piece of thick paper or thin cardboard intended to write on and be mailed without an envelope and at a lower rate than a letter. It is distinguished by stamp collectors from a postcard in that the postage is pre-printed on it whereas a postcard requires a stamp. A postal card is issued by a stamp-issuing authority (typically a country) whereas a postcard is usually printed by a private company, individual or organisation.
In the art-world the postcard can also be transferred into an art-object. The artform where this is done is called mail art.
The collection of postcards is called deltiolgy.
Postcards had a long pre-history before they hit it big, but their breakout came in 1893 at the World Columbian Exposition in Chicago, Illinois. Shortly thereafter the United States federal government, via the United States Postal Service, allowed printers--for the first--to publish 1-cent postcards, although the correspondent's writing was only allowed on the front.
"Undivided back" cards with the word "Post Card" printed on the back (the side without the picture) came in 1901, although writing was still restricted to the front. This is what gives the era it's name. The back was not yet divided into a space for writing and a space for the recipient's address.
The "divided back" card came into use in 1907 with the approval of the United States Postal Service. This era--the Golden Age of American postcards--lasted until about 1915, and ended because of the war in Europe, which affected the business because of increasing war-related tariffs and because many of the country's postcards were printed in Germany or other parts of Europe, which were believed to have better printing methods.
The "white border" era, named for obvious reasons, lasted from about 1916 to 1930. The "linen card" era lasted from about 1930 to 1945, when cards were primarily printed on papers with a high rag content. The last era, beginning in about 1939 and the one we are still in today is the "photochrome" or "chrome" era. The images on these cards are generally based on photographs, rather than paintings or illustrations, and are marked by their extremely glossy appearance.
Smithsonian: Chronology of the Picture PostcardBrief History of Postcards in the United States
External Links
Lisa's Postcard Page
History of Postcard Rates