In addition to Gold, Gems in Guild Wars 2 are the second most important currency. You can redeem them in the game against various other things such as Gold.
Guild Wars 2: 2000 Gems Card
Guild Wars 2 2000 Gems Card (PC) ArenaNet Key - GLOBAL
Guild Wars 2: Secret of the Obscure DLC EN/DE/FR/ES Global
Guild Wars 2: Heart of Thorns + Path of Fire - Bundle DLC EN/DE/FR/ES Global
Guild Wars 2: Path of Fire DLC EN/DE/FR EU
Guild Wars 2: Secret of the Obscure DLC EN/DE/FR/ES EU
