Professional negligence refers to the negligent acts of a medical provider.  This can include doctors, nurses, caregivers, dentists and other health related professionals.  A claim for professional malpractice basically asserts that the professional involved failed to act like other professionals would have acted in the same of similar circumstances.  For example, if you go to the doctor to have a toe removed from your left foot and the toe is removed from your right foot, that surgeon failed to act like a reasonably competent surgeon in the same or similar circumstance.