Potions are a series of consumable items that can only be used once. Potions can be found in the shop during the resting period between two bosses.
Each player has only two slot for placing their potions in, but can stack potions of the same kind in the same slot. Of course, there is a cap on how many of the same potion you can carry and some of them come in stacks of two or more.
Available Potions are (mouseover for description):