Any act or omission which falls short of the standard to be expected of the "reasonable person". For a claim in negligence to succeed, it is necessary to establish that a duty of care was owed by the defendant to the claimant, that the duty was breached, that the claimant's loss was caused by the breach of duty and that the loss fell within the scope of the defendant's duty and was a foreseeable consequence of the breach of duty.

For more information, see Practice note, Claims in negligence: an overview.