The word "negligence" does not define a thing; it refers to a relation. Negligence is defined in the law as the lack of ordinary case. It is a failure to use that degree of care that a reasonably prudent person would have used under the same circumstances.
A broad range of cases involve determining whether a party causing injury was negligent. These cases include motor vehicle, trucking, pedestrian, medical malpractice, premises and boating accidents.
Negligence arises from a breach of a legal duty. For example, a motorist owes a duty of care to other motorists, pedestrians, bicyclists and motorcyclists. The failure to use due care is a breach of the legal duty of care.