What is a green card?

A green card is referred to as evidence of eligibility for permanent residence in the United States, as indicated by the requirement to provide a permanent green card for this purpose ^[2]. Additionally, it is mentioned in the context of obtaining various documents, including visas and passports, which may be necessary for official travel ^[6]. However, the sources do not provide a detailed definition or explanation of the green card itself, leaving some gaps in understanding its full implications and processes.