A postcard or post card is a piece of thick paper and/or thin cardboard, typically rectangular, intended for writing and mailing without an envelope. Non-rectangular shapes may also be used but are rare. There are novelty exceptions, such as wooden postcards, copper postcards sold in the Copper Country of the U.S. state of Michigan, and coconut "postcards" from tropical islands[clarification needed].
In some places, one can send a postcard for a lower fee than a letter. Stamp collectors distinguish between postcards (which require a postage stamp) and postal cards (which have the postage pre-printed on them). While a postcard is usually printed and sold by a private company, individual or organization, a postal card is issued by the relevant postal authority (often with pre-printed postage).
Production of postcards blossomed in the late 19th and early 20th centuries. As an easy and quick way for individuals to communicate, they became extremely popular. The study and collecting of postcards is termed deltiology (from Greek deltion, small writing tablet, and English -logy, the study of).