What citizenship is really about..
Loss of Citizenship
There are two very known ways to lose your citizenship, one of them is expatriation and the other is denaturalization. Expatriation is the legal process by which a loss of citizenship occurs. Expatriation is a voluntary act. The second way to lose your citizenship is denaturalization. Denaturalization is the process by which citizens can lose their citizenship involuntarily. It can only occur by court order and only after it has been shown that the person became a citizen by fraud or deception.
A legal alien a non-citizen who is legally permitted to remain in a country. This is a very broad category which includes tourists, guest workers, legal permanent residents and student visa resident aliens.