Bag slots are an area of the Interface Bar, usually at the bottom-right of the screen, contains five slots for bag items. Some people considered the key ring button part of this area, but it has since been removed.
Your inventory in the game. All items not equipped on your character are stored here. One backpack is automatically provided for you. To fill the other four slots, you must purchase, find, or make additioal bags.
While the bar has five slots only four are changeable, the slot at the right-most end of the interface bar contains the backpack, which cannot be removed or replaced.
Each character can purchase up to seven bag slots in the bank. The cost of the bag slots in the bank increases with each extra slot purchased, starting at 10, then increasing to 1, then 10, then 25, then 25, then 25, then 25, for a total of 111 10 for all seven slots.
Empty bag slots that do not have a bag equipped cannot hold items (other than bags).