Post card is a piece of thick paper or thin cardboard, usually rectangular in shape, written without an envelope. When mailed, it is common to write a short message with the delivery address on one side while the reverse side shows a nice picture. Many postcards are sent when people travel and want to share the local scene without writing a page-long letter. They are quick and efficient to get a message out and do not require an envelope to mail them, which makes them unique to the mailing system.