In the law of negligence which applies to accident and injury cases, a person has acted negligently if he or she has departed from the conduct expected of a reasonably prudent person acting under the same or similar circumstances. The hypothetical "reasonable person" provides an objective by which the conduct of others is judged by the court.
For example, a "reasonable person", knowing that their driveway and walkway is covered with ice and snow would be expected to take reasonable steps to remove the ice and snow through some reasonable measure such as application of salt or sand. If they fail to do so, they can be held liable and would have to pay monetary damages to anyone hurt in their property because of their negligence.