Here is a list of terms used in the medieval sources, with, as best we understand them, their definitions.
 

Carucate The area that a team of 8 oxen can plough in a season. About 120 acres.
Deforciant One of the parties to a court action. The action is brought by the querent, and defended by the deforciant. However the action was often brought to court simply to record an agreement, rather than being contested.
Furlong Originally, the length of a single ploughed furrow, before the plough was turned. Gradually standardised to 220 yards. Locally, the term 'furlong' seems also to have been used for a unit of arable land, typically about 30 acres, divided into strips worked by different people; it is possible that this land unit would have been typically about 220 yards wide, by say 660 yards long (to be investigated).
Heir The person who would inherit a person's main property. This was almost always the oldest son, if the person had any sons; under the terms of Norman inheritance, younger sons and daughters did not normally inherit land. If there were no sons, the daughters would beinherit equal portions. In medieval documents, it is very important to distinguish between the terms "heir of the body", which is limited to the person's children, and "heir" which in the absence of children can be widened to include brothers, nephews, and cousins.
Hide A unit of area, approximately the same as a carucate (which is the area a team of 8 oxen can plough in a season, about 120 acres). A hide seems originally to have been a standard subdivision of the total area of a county, but lost this meaning.
Knight's fee A measure of the military service for which land was granted. Most manors were equivalent to  the service of a single knight's fee, which meant the provision of one knight, with support, for 40 days per year.
Manor This was a land-holding - a manor would normally include a village, with its farm houses, mills, land and streams, but by no means always included a manor house. Manors were the main units of land-holding in medieval England. Each manor would have a "Lord of the Manor" who was granted his holding in return for service (normally but not always military service). This service was rendered to the Lord in Chief, who might be the King in some cases, or a Duke or Earl, or a senior churchman. Many such people held multiple manors, so could not live at all of them and spent much time away anyway on the king's service - so they would normally employ a bailiff to look after their interests.
Marc A unit of money. After 1066, a marc was worth two-thirds of a pound.
Messuage A dwelling-house with its curtilege (outbuildings, courtyards, garden, orchard etc.).
Oyer and terminer A commission of "oyer and terminer" is an appointment as judge for a particular case. The words are medieval French, and simply mean "hear and determine".
Plaintiff One of the parties to a court action - the person who brings the action. There seems to have been some technical difference between a "plaintiff" and a "querent", but it is not now obvious.
Protection A number of references provide "protection with clause volumus" or "protection with clause nolumus" to individuals, normally when they are outside England on royal service (for example military or diplomatic). The protection provided by the crown is not any form of physical protection for the person travelling abroad, but rather of protection against legal process against the person while he/she is abroad. So the person is protected against being sued or prosecuted while they are away. The exact details of the protection differ according to the legal clause attached to the reference - the Latin words "volumus" and "nolumus" are short-hand for two common types of protection.
Querent One of the parties to a court action. The action is brought by the querent, and defended by the deforciant. However the action was often brought to court simply to record an agreement, rather than being contested.
Service That which is owed to a Chief Lord in exchange for the grant of land. This was normally military service (measured in "knight's fees", but could be other types of service, such as the provision of water to the King's court (as was the case for the Newburgh's for Winfrith).
Tenement This was just a generic term for anything held. Normally it meant land and/or buildings that were held. They could be held either as a tenancy (for life or a fixed period of years), or as inheritable property. A manor is a type of holding, but tenement was more commonly used to mean parts of a manor that had been granted out by the lord of the manor.
Tenent/Tenant The person who currently holds a piece of land, normally by occupying it and using it. If this person holds the land directly from the king, the person is called "tenant in chief".
Virgate The area ploughable by two oxen in a season. About 30 acres.