Raku is a type of pottery produced by a very fast firing process. Raku pots are used in some Japanese Tea ceremonies. In the early 16th century, a potter named Chojiro, son of a Korean tile maker, produced vessels that became popular for tea ceremony use in Japan. The Japanese emperor presented Chojiro's brother a gold seal honoring Chojiro in appreciation of the Raku ware. The ideograph 'Raku' was on the gold seal and it means contentment, pleasure and/ or happiness. (Robert Piepenburg, Raku In Japan , Collier Books 1972/1976, ISBN 0-02-011860-0).
Paul Soldner has written additional interesting backgound, available on his site.
The firing technique and the ware produced has become popular around the world. One can achieve a variety of results and a lot of fun.