Geld, specifically the Danegeld, represents one of the earliest systems of direct taxation in Western Europe. Originally instituted as an emergency tribute to buy off Viking raiders during the reign of Æthelred the Unready, it evolved under Cnut and the Norman kings into a regularized land tax. The assessment was based on the 'hide,' a unit of land measurement theoretically sufficient to support one peasant household, though it increasingly became a fiscal abstraction used to determine the military and financial liability of the landholder to the Crown.
In the context of the Domesday Book of 1086, the phrase 'se defendebat pro' (it answered for) indicates the number of hides for which a manor was liable for geld. The right to collect geld or to be exempt from it was a significant mark of status and royal favor among the nobility. While specifically fiscal, the administration of geld reinforced the feudal hierarchy, as tenants-in-chief were responsible for the collection and payment of the tax from their sub-tenants to the King's exchequer. It remained a primary source of royal revenue until it was superseded by newer forms of taxation, such as carucage and scutage, in the late 12th century.