In this context:
42 USC ยง 9102(18)
Discussion
What is that?
The legal definition in the US of what a citizen is. Here: https://www.law.cornell.edu/definitions/uscode.php?width=840&height=800&iframe=true&def_id=42-USC-630966247-802284531&term_occur=999&term_src=title:42:chapter:99:section:9102