As for me, Feudalism was some kind of tradition in medieval Europe. The highest time for it was between 9th and 15th centuries. It combined military and legal customs in a specific way, thus structuring society around the relationships of holding land in exchange for labor. The origin of the word comes from Latin ‘feodum’ or ‘feudum’ (fief). The system, though, had nothing in common with the formal political system. This system was rather a legal or military obligation among the warriors, circulating around three well-known concepts of lords, fiefs, and vassals.
If you want to describe feudalism more broadly, than beside the obligations of the warrior nobility you should mention the three estates of the regality, which are the clergy, the nobility, and the peasantry. Those three were tightly bound by manorialism. Those sometimes referred to be a ‘feudal society.’
To be true, if you are looking for a definition, which would generally be accepted by scholars nowadays, you’d probably get upset. There is no such a thing. The adjective ‘feudal’ first appeared in the 17th century, and the noun ‘feudalism’ was used in 19th century for the first time. The word probably comes from French ‘féodalité,’ which occurred to be created in the 18th century. No wonder, nowadays we have the ongoing discussion of whether feudalism is a useful tradition to study when trying to understand the medieval society.
So, that’s what you probably need to have a good start. Still, if you need more information, I would suggest you look through these papers: