An audit is a systematic and documented process for obtaining evidence that requirements and procedures are being met.
"Clinical Audit is a quality improvement process that aims to improve patient care and outcomes by carrying out a systematic review and implementing change. Clinical audit, when it is conducted well, provides a way in which the quality of care can be reviewed objectively, within an approach which is supportive and developmental."
For more information see Jones 2007 (PDF) or Morell (1999) in the References.