The tangram (Chinese: 七巧板; pinyin: qīqiǎobǎn; literally: 'seven boards of skill') is a dissection puzzle consisting of seven flat shapes, called tans, which are put together to form shapes. The objective of the puzzle is to form a certain shape (given only an outline or silhouette) using all seven pieces, which can not overlap. It is reputed to have been invented in China during the Song Dynasty, and then carried over to Europe by trading ships in the early 19th century. It became very popular in Europe for a time then, and then again during World War I. It is one of the most popular dissection puzzles in the world. A Chinese psychologist has termed the tangram "the earliest psychological test in the world".