A material comprising white clay, or "kaolin," and a feldspathic rock, that react when fired so the clay serves to hold the shape of the object and the rock fuses into a natural glass. In China, it includes any such ware that is highly fired enough to produce a ringing sound when struck. In Europe, it is limited to hard-fired ceramic that is translucent.

Source: AAT

http://vocab.getty.edu/page/aat/300010662