A serf is a laborer who is bound to the land. Serfs differ from slaves in that serfs cannot be sold apart from the land which they work.

Serfs provided most of the labor in feudal society. Most European countries ended the practice of serfdom in the Middle Ages, but Russia retained the practice until February 19, 1861. Parts of Europe, including much of Scandinavia, never adopted feudal instutions, including serfdom.

Nowadays, serf is more commonly used in context with Microsoft, namely Microserf. The noun Microserf applies to employees of Microsoft Corporation, with the connotation that they are tied to that corporation, not the land, and are worked long and hard for the benefit of their masters.