The term 'Green Card, informally' can be summarized as an American Express (AMEX) card. This is a type of credit card issued by the American Express company, which is one of the largest credit card issuers in the world. The card is typically used for purchases and cash advances, and it is accepted at millions of locations worldwide. The card is also known for its rewards program, which offers points for every dollar spent. The Green Card is a popular choice among consumers due to its low interest rates and generous rewards program.