In medieval Europe, a demesne was the part of a lord's land that he kept for his own use. These days, it's more often used to mean "property" or "territory."
The term demesne was originally used to distinguish land totally controlled by a lord from areas that were turned over to tenants. Demesne lands were often farmed and tended by serfs, with the profits or crops going to the lord and his family. Demesne comes from the Latin dominicus, "belonging to a master," and its root domus, "house," which it shares with domicile.