Considering nationality when you are preparing taxes (Nonimmigrant)

Nonimmigrant is someone who seeks temporary entry to the United States for a specific purpose. A nonimmigrant visa allows a nonimmigrant to enter the United States in one of several different categories, which correspond to the purpose for which the nonimmigrant is being admitted to the United States. For example, a foreign student will usually enter the United States on an F-1 visa, a visitor for business on a B-1 visa, an exchange visitor (including students, teachers, researches, trainees, physicians, au pairs, and others) on a 

J-1 visa, a diplomat on a A or G visa, etc. The categories of nonimmigrant visas correspond exactly to the "nonimmigrant status" assigned to each nonimmigrant upon his arrival, based on the purpose for which the nonimmigrant was admitted to the United States. For example, a foreign student who enters the United States on an F-1 visa is considered to be in F-1 student status after he enters the United States; and he will remain in that status until he violates the conditions prescribed for that status, or until he changes to another nonimmigrant or immigrant status with USCIS permission, or until he leaves the United States.

When someone is considered Illegal Alien

An Illegal Alien, also known as an "Undocumented Alien" is an alien who has entered the united States illegally and is deportable if apprehended, or an alien who entered the United States legally but who has fallen "out of status" and is deportable.
An Alien is an individual who is not a U.S. citizen or U.S. National, however an alien is an immigrant who has been granted the right by the United States Citizenship and Immigration Services (USCIS) to reside PERMANENTLY in the United States and work WITHOUT RESTRICTIONS in the United States, there is no "Illegal" alien or "Undocumented" alien. It's just an expression used to talk about someone who is inside the United States without permission.

Considering nationality when you are preparing taxes (part 2)

• A U.S. National is an individual who owes his sole allegiance to the United States, including all U.S. citizens, and including some individuals who are not U.S. citizens. For tax purposes the term "U.S. National" refers to individuals who were born in American Samoa or the Commonwealth of the Northern Mariana Islands.
• An alien is an individual who is not a U.S. citizen or U.S. national. An Immigrant is an alien who has been granted the right by the United States Citizenship and Immigration Services (USCIS) to reside permanently in the United States and to work without restrictions in the United States. Also known as a Lawful Permanent Resident (LPR). All immigrants are eventually issued a "Green Card" (USCIS Form I-551), which is the evidence  of the alien's LPR status. LPR's who are awaiting the issuance of their Green Cards may bear an I-551 stamp in their foreign passports.

Considering nationality when you are preparing taxes

• Nationality:
• U.S. Citizen:
• An individual born in the United States;
• An individual whose parent is a U.S. citizen;
• A former alien who has been naturalized as a U.S. citizen;
• An individual born in Puerto Rico;
• An individual born in Guam;
• An individual born in the U.S. Virgin Islands.
• The Child Citizenship Act, which applies to both adopted and biological children of U.S. citizens, amends section 320 of the Immigration and Nationality Act (INA) to provide for the automatic acquisition of U.S. citizenship when certain conditions have been met.
• One parent is a U.S. citizen by birth or through naturalization;
• The child is under the age of 18;
• The child is residing in the United States as a lawful permanent resident alien and is int the legal and physical custody of the U.S. citizen parent;
• If the child is adopted, the adoption must be final.