From Shadow Era Wiki

Support cards are a type of ability card in Shadow Era.

As opposed to normal abilities, which are one use cards, Support abilities stay on the field for a certain of turns depending on the card, and give the player different effects while there. Starting with Dark Prophecies, Support cards began using the Duration keyword to show how many turns they stay on the field. While these cards will eventually remove themselves from the field, they can also be destroyed by card effects that can destroy such abilities.