Which of the following best describes negligence?

Negligence is a legal concept that occurs when an individual fails to exercise the appropriate level of care that a reasonably prudent person would in similar circumstances, leading to harm or damage to another person. This definition emphasizes the aspect of carelessness rather than malicious intent, which sets it apart from other forms of liability like intentional torts.

In this context, the correct choice captures that essence by highlighting that negligence involves a failure to use reasonable care, which contributes directly to causing harm. The emphasis on 'reasonable care' underscores the standard expected in various situations, indicating that negligence is determined based on what would be considered appropriate behavior in that specific context.

The other choices do not adequately represent negligence. An intentional act causing harm describes a different legal basis known as an intentional tort. An unavoidable accident is typically recognized as a situation where no party is at fault, thus lacking the element of negligence. Lastly, the notion that an act must always be committed knowingly aligns with intentional behaviors, which again deviates from the fundamental principles of negligence that hinge on a lack of care, rather than intention.