Feudalism is the term used hereafter to describe the societal structure of the Seven Kingdoms, as it largely resembles the real life Feudal system of medieval Europe.
Feudalism was introduced to Westeros by the Andal traditions and is practised within the borders of the Seven Kingdoms. This society is based on a rigid social structure and government consisted of kings, lords, and the peasants. Nobles rule over the smallfolk within their territory through a system of fealty and sworn oaths, in this system each man owes military service to his lord in return for protection, a grant of land, and the peasants to work it.
The feudal system has rigid structure of social classes. Those who are born Commoners can expect to die as Commoners. There are no provisions for the advancement of individuals from a lower class into the higher classes. This is not to say that it is impossible, only that it is very difficult, usually bestowed by lords to those who have done a great service to them, or Knights bestow the rank and title of Knighthood on any individual who has proven himself worthy.
The king, in our case the King on the Iron Throne, is at the top of the pyramid; beneath him are the various lords and knights, with peasants, also known as smallfolk, at the bottom. The king sits on the Iron Throne, claims ownership of the land, has the final political authority and holds the ultimate power in all matters. Although in practice the king is constrained by political realities, and while no individual command is likely to be countermanded, he could still lose his position to intrigue if he were to offend the wrong people. Of course, as kings do not retire, this loss of position would involve his death.
Kings in turn have Vassals, the high Lords of great houses. These high Lords control the major regions of the Seven Kingdoms, and in turn employ Vassals of their own; even these lords might have vassal lords sworn to them. This system terminates with the lowest level subordinate knights or minor land owners.
In GRRM world there are only lords, some bigger and some smaller, some sworn to others, but still all with the same title - save for the Lords of Sunspear, who still hold the title of "Prince." Nobility is a hereditary title, that it is expressed through the bonds of vassalage which connect between them the various owners of strongholds. Each lords have vassals, the vassals have vassals, and sometimes the vassals of the vassals have vassals, down to the guy who can raise five friends.
With the lord of the great house at the top, holding dominion over one of the nine regions of the seven kingdoms, second only to the king and petty lords at the bottom, that entrusted with only a few villages. It is the Lord's responsibility to see to the affairs of his lands, keep the King's peace, judge on local matters, and ensure that taxes due to the King are collected in a timely manner.
Steward: the man responsible for running the day-to-day affairs of the castle and acting on the lord's behalf. He may be entrusted with the castle in the lord's absence.
Knights are the lowest rank of the nobility, this class is made of Landed knight, who have been given a keep and grant of land to administer. They have their own peasants and men-at-arms, and may even take sworn swords. Landed knights are sworn to fight for the lord who holds dominion over their land. While the wealthiest knights manage more land than the poorest lords, landed knights do not have the authority to deliver justice in their land. Rather, they must appeal to their liege lord.
Commoners or Smallfolk are the bottom of the social structure. They don't own lands or titles; they work the land of their lords, and don't have a say in their own governing. While this may seem similar to slavery, the difference is that commoners own themselves, and can make appeal to their local lord regarding violations of the law or general disagreements between parties; they are recognized as having a right to fair and just treatment by the nobility and society in general. Most Houses have laws protecting the local population from abuse or mistreatment, even by members of the nobility. However those laws differ and are enforced in varying degrees, mostly depending on the disposition of the local lord.
Many of the tradesmen and craftsmen belong to guilds (notably the alchemists).
There is little social mobility; odds are that if you are born a commoner, you'll never be able to rise above commoner status. However, it does happen, and there several examples of people who have managed it. Varys was a common-born slave, and rose to be the spymaster of the Seven Kingdoms. Petyr Baelish was born a minor noble, almost a commoner, yet he was able to rise to be a member of the King's Small Council.
- Wardens: exercise military functions and are nominated for each of the borders in the Seven Kingdoms.
- Liege: primary lord of a vassal who holds by military tenure. The liege lord and vassal each have responsibilities to one another; the vassal must remain loyal to the liege lord above any other lords, while the liege is the vassal's principal protector.
- Vassal: A person granted the use of land, in return for rendering homage, fealty, and usually military service or its equivalent to a lord or other superior. They are frequently referred to as "bannermen'.