a person who is a member of a nation and is entitled to its protection is a citizen.
In a nation, a citizen has to follow the laws implemented and introduced by the government, and is entitled to the rights and privileges the government guarantees.
In the US , a person can become a citizen by being born on US soil, and outside to a parent who is a US citizen.
Citizen can be defined as a legally recognized subject or national of a state or commonwealth, either native or naturalized.