What is the meaning of "Green Card" in the United States?

The U.S. green card, also known as the U.S. permanent resident card, is an identity document used to prove that foreigners have permanent resident status in the United States.

Lawful permanent residence for green card holders is an official immigration benefit, which includes conditional permission to reside and work in the United States. The holder must maintain his or her permanent resident status and may lose it if one of the conditions required for the status is no longer met.

U.S. permanent residents are not U.S. citizens and still have the nationality and passport of their home country, but their permanent resident status allows them to freely enter and exit the United States, live and work in the United States indefinitely, and meet the requirements for residence time in the United States. You can then apply to become a U.S. citizen.

Extended information:

U.S. green card validity period: A legal permanent resident has lived in the United States as a permanent resident for 5 years (or 3 years after marrying a U.S. citizen), and Once you meet all the requirements listed by the USCIS, you can apply to become a U.S. citizen. Citizens will have more rights (and obligations) than permanent residents (who are still considered foreigners in this regard).

Some of these rights include: the right to vote; the right to stand for election in federal and state elections; the ability to bring family members to the United States; and the ability to hold federal office. Other citizenship benefits include visa-free access to select countries around the world. Certain circumstances that would subject permanent residents to deportation proceedings also do not apply to U.S. citizens.

Reference: Baidu Encyclopedia-US Permanent Resident Card