A "green card" is the common term used for a US permanent resident card (or permanent residence visa). It allows you to live and work permanently and legally in the United States.
A green card, known officially as a Permanent Resident Card, is a document (card) issued to immigrants to the United States under the Immigration and Nationality Act (INA) as proof that the holder has been granted the right of living permanently in the US. Holders of green cards are known as Lawful Permanent Residents or green card holders.
Green card holders can apply for US citizenship if they can prove that they have continuously lived in the US for at least five years.
The US Government issues to every lawful permanent resident a permanent resident card, which is commonly called a "green card." The origin of this name is the card’s historical green color.