Supreme Court Justice Horace Gray explained the difference in his ruling in U.S. v. Wong Kim Ark in 1898: “Subject’ and ‘citizen’ are, in a degree, convertible terms as applied to natives; and though the term ‘citizen’ seems to be appropriate to republican freemen, yet we are, equally with the inhabitants of all other countries, ’subjects,’ for we are equally bound by allegiance and subjection to the government and law of the land.”
A “subject” is essentially owned property.