Feudalism was the name of the most common social structure in Europe during the dark ages.
(other forms are called democracy, communism, socialism, theocracy, monarchy...)
Most of the people in the feudal system were "peasants," which was just another word for slavery.
If you were born in a certain area, you were required by law to stay there all of your life and work for the Landlord. Chivalry was what they called it when the rich people were polite to each other.

I know, this is a gross oversimplification. You'll get more in History class.
Can anyone do better, short of writing a book?