Serfs are a class of people who are indentured servants but are not slaves. They live on landowners property, and are allowed to farm the land which they are allotted by their landlords. Each harvest, serfs were expected to provide a certain pre-negotiated amount of food to their landlord in exchange for the use of their land.
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However, many times these amounts of food were often too large to be able to be met by serfs, causing them to become stuck in the cycle of debt and work, which any children they might have would also be born into.