When you get an item, you will see "Character Bound" under the item's name. Character bound means that the item only can be used if you choose a target to use the item. There are two kinds, character bound with red color and character bound with green color. What is the meaning of it?
Simple, the red one means
you get this item from event or quest, so you can't trade or sell it. As for the green one, you can trade it to any other players or sell it.