A postcard or post card is a rectangular piece of thick paper or thin cardboard intended for writing and mailing without an envelope. Shapes other than rectangular may also be used. There are novelty exceptions, such as wood postcards, made of thin wood, and copper postcards sold in the Copper Country of the U.S. state of Michigan, and coconut "postcards" from tropical islands. The world's oldest postcard was sent in 1840 to the writer Theodore Hook from Fulham in London, England. The study and collecting of postcards is termed deltiology.