"Validation" is a process where an independent third party (a Designated Operational Entity: DOE) access the project design document (PDD), which is prepared by the project participants to determine the project's eligibility as a CDM project. After a project is evaluated valid by the DOE, it is submitted to the CDM Executive Board to be registered as an official CDM project.
Verification is to check periodically the amount of Green House Gas emissions for a CDM project activity, which is operating and is registered by the CDM Executive Board.