Non-monotonic reasoning is a type of logical reasoning where the introduction of new information can change previous conclusions. Unlike traditional logic, where once something is proven true it remains true, non-monotonic reasoning allows for flexibility. This is useful in real-world situations where knowledge is incomplete or evolving. For example, if we know that all birds can fly, we might conclude that a penguin can fly. However, upon learning that penguins are a type of bird that cannot fly, we revise our conclusion. This adaptability makes non-monotonic reasoning important in fields like artificial intelligence and knowledge representation.