A negligent act refers to a failure to exercise the care that a reasonably prudent person would under similar circumstances, leading to unintended harm or damage to another party. This concept is essential in establishing liability in tort law, where the focus is on the breach of duty and the causation of harm resulting from that breach. Understanding how intervening and superseding causes can affect liability is crucial, as they can either break the chain of causation or mitigate the responsibility of the original negligent party.