Satsuma (or "Satsuma ware") is a type of Japanese ceramics produced in the Satsuma region of Kyushu Island, Japan. Satsuma ware is produced at lower temperatures than porcelain, yet at higher temperatures than most pottery, so in a way, it is half-way between the two. The central characteristic of Satsuma ware is the richness of its decoration, usually executed in gold and polychrome colours (in later Satsuma ware, one particularly sees a unique blue glaze, Gosu blue) on a background of crackled white glaze.
The first Satsuma ware was produced using imported Korean techniques, using local (brown) clay. By the second half of the 18th century, the Satsuma ceramics had become so popular that clay was freighted from Kyushu to Awata near Kyoto, where it was used to produce a local variant of Satsuma ware, called "Kyoto Satsuma". Much of this was used as export goods, and wound up in Europe, where it helped inspire (among others) Wedgwood's ceramics works. In particular, the 1867 Paris Exhibition served as a showcase for Satsuma ware.
Today, many second-rate knock-off imitations of authentic Satsuma ware are produced, in China and Korea. Some are even passed off as antiques. In these cases, it is a case of caveat emptor. Usually, however, the copies are of such inferior quality that their nature is clear. When in doubt, contact an expert.