From Elsmar Cove Quality Assurance and Business Standards Wiki
Corrective Action: Actions taken to eliminate the root cause of an existing nonconformance and to prevent its reoccurrence.
Preventive Action: Actions taken to eliminate a 'potential root cause' to a potential problem that has not occurred.
The 'Definitive' discussion of the definition of Preventive Action is in the thread Corrective Action vs. Preventive (Predictive) Action - A Definitive Discussion
For additional discussions, see Preventive Action and Continuous Improvement
