Answer
In the context of the ISM Code and Quality Management Systems (QMS):
Correction: Fixing the immediate problem (treating the symptom).
Example: Cleaning up an oil spill from a leaking pipe and tightening the flange.
Corrective Action: Identifying and eliminating the root cause of an existing non-conformity to prevent it from happening again.
Example: Investigating the leak, discovering the flange material was incorrect for the pressure, and replacing all similar flanges onboard with the correct specification.
Preventive Action: Identifying a potential non-conformity and eliminating its cause before it ever happens.
Example: Reviewing industry safety bulletins, realizing sister ships have vibration issues in a specific pipe, and modifying the pipe supports on your vessel before any leak occurs.