A nonperson is a citizen or a member of a group who lacks, loses, or is forcibly denied social or legal status, especially basic human rights, or who effectively ceases to have a record of their existence within a society (damnatio memoriae), from a point of view of traceability, documentation, or existence.
Seems to overlap with the (to me) far more familiar "unperson" - a term which I think Orwell may have coined.
Regards,