Feudalism

Feudalism arose at a time when central governments were weak or nonexistent in Europe, and kings used the system to exert control over their subjects and secure military strength throughout their lands. In the absence of a strong monarchy and rule of law, the feudal relationship between the lord and his vassal was the glue that held medieval society together.
"http://historymedren.about.com/od/feudalism/a/feudalism.htm"

This is the simplified version of definition, and there are a lot more better explanations and exceptions that go along this medieval history. It is fair to say that this is the explanation you read from the textbooks and the dictionary.
But the problem is.......
Nearly none of them are accurate.
Feudalism was NOT the "dominant form of political organization in medieval Europe.
"http://historymedren.about.com/od/feudalism/a/feudalism.htm"
I read something similar like this before somewhere and there was no "hierarchical system" of lords and vassals like we like to think. Manorialism or Seignorialism was not part of a Feudal System.
Kings did NOT use Feudalism to exert control over their subject, and the feudal relationship was NOT the "glue that held medieval society together.
"http://historymedren.about.com/od/feudalism/a/feudalism.htm"