Latin, castellaria, castellatus.
A castlery was a block of territory attached to a castle or within its jurisdiction. Domesday Book names fourteen, most of them substantial. Count Alan of Brittany's castlery of Richmond, for instance, contained 199 manors, and three of the Rapes of Sussex each contained over a hundred manors. Although only the Rape of Hastings is actually called a castlery in Domesday (SSX 9,11), all the Rapes were probably castleries since all centred upon a major castle from which the Rape derived its name.
Domesday's terminology is, as usual, inconsistent. Some castleries were called territories (divisio or leuga in Latin), and others, like Monmouth, simply castles. Others were certainly unnamed: there were many more castleries than have been identified at present.
All castleries and territories in Domesday were in vulnerable border counties: coastal areas, the Welsh border, and Yorkshire and the north (border areas for much of the Conqueror's reign).
For more detail, see John le Patourel, The Norman Empire (1976); and Judith A. Green, The aristocracy of Norman England (1997).