green card

Short definition from Wiktionary

Noun

1. 1
   A US work permit, officially known as United States Permanent Resident Card.
2. 2
   A warning card, given to a player for an infraction of the rules. A further infraction may warrant a yellow card or red card.
3. 3
   A chargecard launched by American Express in 1969.
4. 4
   Used other than figuratively or idiomatically: see green, card.