Duplication

Duplication (also known as duping) is a process when the player "clones" an item and how many you have of it to make the game easier.

Many players of Terraria do not support duplication when playing the main game and mostly use it for PvP. Duping Fallen Stars is very useful for using the Star Cannon.

Duplication has now reached the console versions of Terraria also.

PC Duplication
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Console Duplication
As far as Console Duplication goes I only believe you can only dupe on Xbox 360. It can be done on single player and multiplayer. The multiplayer method is quicker and the single player process is quite lengthy.