Latin, terra ... carucis.
In agricultural terms, the ploughland was the amount of land which could be ploughed by an eight-oxen plough team in the course of the year. In many counties - notably in those of circuit 3 - the statistics illustrate this to perfection. On manor after manor, the land available for ploughing exactly matches the stated number of ploughs. Where this was not the case, moreover, it was usually recorded that 'there could be' so many more ploughs, this number being the difference between the actual ploughs and the land available for ploughing. Thus, if a manor had 'Land for' 6 ploughs but only 4 actual ploughs, the scribe recorded that 'there could be 2 more ploughs there'.
However,in other counties there are no such neat equations, carucates, ploughs or plough teams bearing artificially fixed ratios to each other, suggesting that the ploughland figures might be a fiscal assessment as well as a estimate of arable land.
The arguments for this interpretation are clearly laid out in two articles by Sally P.J. Harvey, 'Taxation and the ploughland in Domesday Book', Domesday Book: a reassessment, edited by Peter H. Sawyer (1985), pages 86-103, and 'Taxation and the economy', in Domesday studies, edited by J.C. Holt (1987), pages 249-64, recently updated and slightly modified in her Domesday: Book of Judgement (2014), pages 223-26, where it is argued that the ploughland was a new fiscal assessment designed to reduce the amount of the exempt demesne of the tenants-in-chief, a view not miles apart from that of David Roffe, that the ploughland was 'a non-fiscal measure of fiscal land' or 'a measure of the capacity of the hidated land to pay the geld assessed upon it: Domesday: the Inquest and the Book (2000), pages 155, 165, and Decoding Domesday (2007), pages 206-207