The term green card is also known as a United States Permanent Resident Card. The card is used as identifications for those who are not native born to the United States. The reason a green card is issued is to show that the person may prove that they are a legal citizen. A green card is need to obtain employment within the United States.
Green cards are issued by the Bureau of Citizenship and Immigration Services, which is part of the Department of Homeland Security. A green card can allow an alien to work while in the United States, and work as a temporary passport to re-enter into the United States. A green card is the fist step to getting a permanent citizenship of the United States.