Naturalization is the acquisition of citizenship

Citizenship

Citizenship is the state of being a citizen of a particular social, political, national, or human resource community. Citizenship status, under social contract theory, carries with it both rights and responsibilities...

 and nationality

Nationality

Nationality is membership of a nation or sovereign state, usually determined by their citizenship, but sometimes by ethnicity or place of residence, or based on their sense of national identity....

 by somebody who was not a citizen of that country at the time of birth.

In general, basic requirements for naturalization are that the applicant hold a legal status as a full-time resident

Permanent residency

Permanent residency refers to a person's visa status: the person is allowed to reside indefinitely within a country of which he or she is not a citizen. A person with such status is known as a permanent resident....

 for a minimum period of time and that the applicant promise to obey and uphold that country's laws, to which an oath or pledge of allegiance is sometimes added.