An item pool is the set of items that can be generated under a given circumstance. There are many item pools that exist within The Binding of Isaac: Rebirth.
- Item pools can be exhausted by having the game create every item in that specific pool. Items don't need to be picked up for this to happen, the game simply has to generate them (rerolling the item with The D6 for example).
- When an item pool is exhausted, the game will generate items from the Treasure Room item pool instead.
- If the Treasure Room pool is exhausted, the only item that can be generated will be Breakfast.
- Specific drops from mini-bosses are specified item drops, not real item pools. Therefore, items from mini-bosses can be repeatedly generated without exhausting their item pools.