Stoneware is a rather broad term for pottery or other ceramics fired at a relatively high temperature. A modern technical definition is a vitreous or semi-vitreous ceramic made primarily from stoneware clay or non-refractory fire clay.
“Stoneware, which, though dense, impermeable and hard enough to resist scratching by a steel point, differs from porcelain because it is more opaque, and normally only partially vitrified. It may be vitreous or semi-vitreous. It is usually coloured grey or brownish because of impurities in the clay used for its manufacture, and is normally glazed.”
Kawai Kanjirō (河井 寛次郎, 24 August 1890 – 18 November 1966) was a Japanese potter and a key figure in mingei(Japanese folk art) and studio pottery movements, he was known one of best mastery in stoneware pottery in his era.