Fame is the currency besides Realm Gold, but unlike Realm Gold, Fame can only be achieved by playing the game itself (You have to die to get it). fame can be spent on feeding pets, fusing pets, pirate rum, drake eggs, and dungeon keys for rare dungeons (such as Bella's Garden and Battle for the Nexus)
Fame can be gathered from defeating monsters (not the easy ones on the beach and next to it). The harder the monsters you fight, the faster you gain fame.
At first, you won't be able to keep track of how much fame you earn. After you reach level 20 (the maximum level), you will see an orange bar replace the green one that shows your experience. This bar shows how much fame you have when you mouse over it, and will fill as you complete the class quests for the particular character you're playing as.