Bing found the following results
Serf - World History Encyclopedia
Serf Definition & Meaning - Merriam-Webster
Serfdom - Wikipedia
Serfdom | History & Examples | Britannica
Serfdom in Europe (article) | Khan Academy
Serf - Definition, Meaning & Synonyms | Vocabulary.com
Serfs and manorialism (video) | Khan Academy
SERF Definition & Meaning | Dictionary.com
Serf | Encyclopedia.com
serfdom summary | Britannica