Sandy Ware is a type of medieval (and earlier) pottery with enough quartz sand mixed in with the clay for it to be visible in the fabric of the pot. The sand acted as a temper which helped bind the clay together, and keep the finished pot from cracking while being dried and subsequently fired. Examples are found across the UK, and have different chronologies in different part of the country.
If you are particularly interested in medieval pottery, and want to learn more, the Medieval Pottery Research Group website has some useful links and a bibliography that should get you started.
The Portable Antiquities Scheme is a project to encourage the voluntary recording of archaeological objects found by members of the public in England and Wales. Because the focus is on small finds reported by the public, there is a bit of a bias towards metalwork (for example this Roman brooch*), but bits of flint (for example this gun flint), pottery, etc. that someone finds "interesting" are also reported and recorded. There are currently some 335 pieces of Sandy Ware on the database.
Archaeologists are fond of using the term "-ware" to differentiate between different pottery types. In London, we also get a type of pottery known as "Shelly-Sandy Ware" which - as you've probably already guessed - used both sand and ground-up shell as temper.
* Examples found by me while assisting at at past public open days at the Tower of London foreshore and reported to the PAS.