The Gift Card allows you to give one of your territories away to another player. This is most useful in team games, where you can give your teammate access to a completely different part of the map.
All armies on the target territory will also be transferred to the target player.
You may only gift territories to players who are still in the game; eliminated players may not be revived.
Gift Cards happen after deployments and airlifts, but before attacks. This means it's okay to airlift into or out of a territory you are gifting on the same turn. However, you should not abandon a territory you are gifting in the same turn, since it will cause the gift to fail.
Any armies that are on the territory when it is gifted are considered used for that turn. That is, they cannot do another attack or transfer in the same turn. Except in multi-attack games, where armies can be moved after they're gifted by the player who received the territory.