A fetter is a shackle or chain that is attached to someone’s ankles. To fetter someone is to restrict their movement, either literally or metaphorically. You might feel fettered by your parents' rules, even without the chains.
A fetter is anything that secures and limits the movement of the feet and legs of a prisoner. To fetter, the verb, could be used literally: the prison wardens would fetter the chain gangs who built many of the railroads in the US., but it usually means something has been done to restrain someone’s behavior: "we finally managed to fetter our sons’ computer use with bribery."