Equipment

The Equipment section of your Inventory contains all of the armor and weapons that you have purchased (including different class gear. This allows you to change your armor and weapons if you wish; however, note that wearing the gear of a different class won't give you any bonuses for attributes such as Strength, Constitution, etc.

See the Class System page for more details.

Costume
If you would like to use certain gear, but don't like the way it looks on your avatar, you can check the "Use Costume box under your gear to customize your avatar's appearance while reaping the benefits of the gear that you have equipped (see Gear above).