Is there any significant difference between slavery as was practised in the United States and serfdom as was practiced in the middle ages of Europe? Not legal technicalities or theoretical differences, but in terms of the day to day reality of life for people with status such as "villains" in England?

I have seen conflicting information in educational sources with some saying that serfs are a form of slave and some sources (typically American ones) saying there is a difference. But it seems the basic principles are the same on the face of it, such as ownership of the person, and the treatment i.e. peasants being killed with impunity after revolts. Is there any definitive answer or is it subjective and shades of grey?