serf, or slave
Servus, translated as slave in the Phillimore edition, is sometimes rendered as serf.
Slaves formed the fourth largest group among the peasantry, over 10% of the recorded population and significantly higher than this if allowance is made for their almost complete omission from the counties of circuit 6. This omission was certainly a quirk of the Return from the northern circuit since slaves appear in considerable numbers in all other counties, and the one satellite text for the circuit reveals that there were slaves on the estates recorded there but not in Domesday Book.
Slaves were at the bottom of the economic and social scale, normally without resources of their own and there to perform their lord's bidding. The significant correlation between numbers of slaves and plough teams on the lord's demesne, or home farm, has been taken to prove that they were often utilised by the lord as his ploughmen.
There has been some discussion as to whether slaves were recorded as individuals or as heads of families. If the recorded slaves were all individuals, they constituted little more than 2% of the population, since the totals for other groups are normally multiplied by a factor of 4-5 on the assumption that the numbers represent heads of families rather than individual peasants. These divergent estimates are of real consequence. The lower figure would certainly help to explain the rapid disappearance of slavery after the Conquest. However, the most recent investigations have concluded that slaves were probably counted on the same basis as other social groups, in which case they formed 10% of the population. In this case, their virtual disappearance within a generation of 1086 was a remarkable social transformation aided, perhaps, by a tendency by lords to endow slaves to perform their ploughing functions as 'free ploughmen'.
For further information, see M.M. Postan, The famulus: the estate labourer in the XIIth and XIIIth centuries (1954); David Pelteret, Slavery in early medieval England from the reign of Alfred until the twelfth century (1995); and J.S. Moore, 'Quot homines?: the population of Domesday England', Anglo-Norman Studies, vol. 19 (1997), pages 307-34.