Everybody sort of knows the term 'feudalism' and figures it has something to do with the Middle Ages. However, medieval scholars no longer use the term. Why is this? you ask (especially since your high school social studies teacher seemed to think it was important).
The problem is that the word 'feudalism' has been used in so many different ways, many of them contradictory, that someone hearing or reading the word has no idea what it means. This is especially a problem because 'feudalism' isn't even a translation of a medieval word, but dates instead to the seventeenth century.
Sometimes the word is used to refer to peasants. Sometimes it refers to knights and nobles. Sometimes it is supposed to date to the sixth century. Sometimes it refers to the Ancien Régime in France (seventeenth and eighteenth centuries). Sometimes it is a legal category. Sometimes it is economic. Sometimes it refers to fighting with swords. But whatever it is supposed to mean, it is always Bad. No wonder medievalists avoid it!
When the word 'feudalism' was first coined (seventeenth century), it meant specifically fiefs (a fief is a feudum in medieval Latin). I will discuss fiefs more in a later post, but basically it was a relationship strictly between knights and nobles, where one man received a piece of land, the fief, from another, in return for loyalty and support (not rent). Fiefs flourished not for the whole Middle Ages but really only in the eleventh through thirteenth centuries.
At the time of the French Revolution, 1789, revolutionaries wanted to end abusive practices of the Ancien Régime, things like hereditary judgeships, noble exemption from royal taxes, and dove cots (many nobles raised doves for food, and the doves flew out and ate peasants' grain). None of these things had anything to do with fiefs or even the Middle Ages. But they were Bad, so the revolutionaries decided to call them 'feudalism,' the word to them meaning Bad Old Practices.
So already the word had two distinct meanings, referring to quite different conditions six centuries apart. Then in the nineteenth century Karl Marx got hold of the word. He decided 'feudalism' was a stage, between slavery (as in ancient Rome) and the rise of the bourgeoisie (in the eighteenth-nineteenth centuries), and that it involved serfs/peasants and began in the sixth century. It was, he felt, very Bad.
As if three different meanings weren't enough (social, legal, economic, sixth century, twelfth century, eighteenth century), the word 'feudalism' has acquired many additional meanings. Powerful local lords, whether warlords in Afghanistan or leaders during the shogun era in Japan, are said to be examples of feudalism. Every sword, every castle, every medieval battle is supposed to be an example of feudalism. Every oppressive landlord is supposed to be practicing feudalism. All of these are Bad.
Make things easy on yourself. Just don't use the word! If you want to discuss peasants, or castles, or fiefs, or warlords, just do so. The only times it makes sense to use the word is if you're talking about the French Revolution, when you might as well use the revolutionaries' definition (just remembering it had nothing to do with the Middle Ages), or if you're discussing the philosophy and writings of Karl Marx. Then at least it's clear what you mean by the word.
(It's not your high school social studies teacher's fault. She was just following the textbook.)