What's the comprising between the serfs and the slaves?

I think that you mean comparison, and I'll try to answer this. Serfs are (it varies depend on culture and time) people who are signed to a lord. they will work for him for 1 or more days a week and then work on their own lands. They will pay taxes, which most lords would avoid paying their own. Slaves are chattel, sold and have nothing to their name. While both are degrading, the slaves have it much worse off.