Like slaves, serfs could be sold and bought, but usually only together with the land they were working on. A serf worked for his landlord without pay and had little rights. They could be abused by their landlords, were not allowed to marry without his permission and were not allowed to leave their land. As a result, serfdom is seen as a form of slavery.
Serfdom was common in Europe and persisted in Russia till 1861, when Tsar Alexander II abolished the practice, thereby freeing about 23 million serfs in a single day!
The image above shows a 1907 painting depicting serfs listening to the proclamation that would give them their freedom.
"The Great World History Book"