I am not able to get into the finer details of the specifics of European serfdom in the same way I can with slavery, but you should find this old answer of mine illuminating, comparing transatlantic slavery with Russian serfdom. It's a very theoretical answer - concerned with why historians call some forms of forced labour 'slavery' and not others - but detailed, and includes some useful sources for further exploration of Russian serfdom if this is a topic of interest to you.