A postcard or post card is a rectangular piece of thick paper or thin cardboard intended for writing and mailing without an envelope. There have been exceptions to this, such as wood postcards, made of thin wood, and copper postcards sold in the Copper Country of the U.S. state of Michigan.In some places, it is possible to send them for a lower fee than for a letter. Stamp collectors distinguish between postcards (which require a stamp) and postal cards (which have the postage pre-printed on them). While a postcard is usually printed by a private company, individual or organization, a postal card is issued by the relevant postal authority. The study and collecting of postcards is termed deltiology.