The following is an extract from www.medievalgenealogy.org.uk
It's useful to know something of the prevailing system of land tenure. In post-conquest medieval England, land was not owned, in the modern sense, by anyone but the monarch. Instead it was held by tenants, from lords (or occasionally ladies) in return for the obligation to perform some service. This was the feudal system, with the king at the top of the ladder, his direct tenants (tenants in chief) beneath him, and lower still under-tenants of various sizes, down to the peasant farmers who held a few acres in return for labouring on the land of the local lord.
The main building block of the feudal system was the manor, an estate on average somewhat smaller than the parish (typically a parish might contain several smaller manors or one larger one, though sizes could vary considerably, and some manors were much bigger). Most frequently the service performed for the king by his tenants was military - in this case feudal holdings were measured as so many knights' fees, according to how many knights the holder of the land was obliged to provide. Land might also be held by serjeanty, that is by some non-military service, often in the royal household, or in the case of religious houses by free alms, that is by spiritual service.
Land held by a lord himself, rather than by his tenants, was known as demesne. The same term describes the royal estates (held by the king rather than his tenants in chief), manors held by tenants in chief rather than under-tenants, and even the part of a manor held by its lord, rather than manorial tenants.
The manor was the building block of feudal society. As such it embodied the 'government' of the local community in medieval times. It not only had administrative control over matters such as the succession to land tenure within the manor, but also often functioned as a local court of law for routine offences. Manorial documents are among the few types of records where genealogical information about ordinary people - rather than the upper classes - is likely to survive from medieval times.
Within the manor, land could be held in several ways. The fullest information in the records is about those who held land by customary tenure, that is, traditionally, in return for labouring on the lord's own land, the demesne. The descent of these holdings was governed by the custom, or accepted rules, of the manor in question - the commonest form of customary tenure, which evolved in late medieval times, was known as copyhold tenure, because each tenant would be given a copy of the entry recording his succession in the manor court roll. Freehold land was held primarily in return for a fixed rent, and its descent was not governed (or recorded) by the manor. However, freeholders were still subject to manorial jurisdiction in other respects, so that they do also appear in the records. Others held leasehold land, usually for a year at a time in the medieval period, but later for longer terms. In general, there was a tendency over time for the rights of the lord to be eroded, and for freehold tenure to become the norm - although the last vestiges of the copyhold system survived until the 20th century.
Generally the most useful manorial records for the genealogist are those of the court baron, which dealt with the everyday business of the manor, meeting typically every 3 or 4 weeks. This business would include the reporting of tenants' deaths - in theory, freehold as well as customary tenants - and the payment to the lord of the corresponding feudal due, called a heriot. When the heir of a dead customary tenant succeeded, the surrender of the land and the admission of the new tenant would be recorded, and the relationship between the two would normally be noted. Occasionally, there are also payments for the marriages of the daughters of customary tenants (merchets) or records of the remarriage of widows. As well as these specific records of the events that are crucial to the genealogist, many tenants will be routinely named for a variety of reasons - they may appear as officials or jurors, they may be noted as absent (with or without leave), or they may be fined (amerced) for some minor offence.
Many manors also held a court leet, which acted as a court of law dealing with routine local matters (and even with capital offences in earlier times). This jurisdiction declined rapidly during Tudor times.
Another important record is the manorial survey. Surveys assumed different forms - and are known by different names - in different periods. Usually they include at least a list of the names of the manorial tenants, and may give much fuller information. The main categories are the custumal, common in the 12th and 13th century, which records the tenants, their holdings and their obligations to the lord; the extent, a valuation of the manor, including the demesne, which seems to have been inspired in the 13th century by official surveys connected with inquisitions post mortem; and rentals, lists of tenants and the rents payable, beginning in the 14th century, when it became common for the lord to rent out the demesne rather than working it himself. Very detailed surveys were also produced in Tudor times. Similar information may also be gleaned from manorial accounts, where they survive. Surveys can obviously be very useful to the genealogist, in that tenants are often associated with an identifiable land-holding, although explicit genealogical information is rare.
Although the focus in manorial documents is on the ordinary tenants, it is worth remembering that they often also identify the lord of the manor. In medieval times, such a dated reference can sometimes provide a useful chronological clue - for example, to the date of the death or remarriage of a widow holding the manor for her life.