The Pinhoes are a family of witches and wizards living in the area near Chrestomanci Castle, principally in the village of Ulverscote. They have intermarried with, and collaborated with, other magic users in the Farleigh and Cleeve families. The Pinhoes seem to specialize in magic involving natural things, such as herbs and woodworking. The Farleighs seem to be more... aggressive in the magic they utilize.
All these families of magic users agree that it's important to conceal their abilities from the most famous enchanter around them, who happens to live right next door in Chrestomanci Castle. They explain to young folks that it's so that nobody will interfere with the important things they do and protect, but it comes out in the course of The Pinhoe Egg that there's a great deal more to the tradition than they even know.