Debuff cure potions are potions that remove debuffs such as paralysis or poison. They are usually sold in alchemist shops but can also be found strewn about in caves, storehouses, or sometimes randomly in the middle of regions without many enemies. It is advised that you stock up on these, especially before going into dungeons or regions like the Fen of Death and Silver Glades.
If you fail to stock up on these, you can, and likely will be paralyzed and poisoned for long and uncomfortable chunks of time.