Default reasoning is a type of logical reasoning used when there is incomplete information. It allows individuals to make assumptions based on typical or common scenarios, filling in gaps when specific details are missing. This approach is often used in everyday decision-making and problem-solving. In artificial intelligence, default reasoning helps systems make inferences about situations where not all facts are known. For example, if a system knows that birds typically fly, it might assume that a sparrow can fly unless there is evidence to suggest otherwise. This method helps streamline reasoning processes in uncertain environments.