A review is a formal inspection of developmental progress, generally for the purpose of obtaining concurrence from an Acquisition Customer that work done to date indicates that the final product is reasonably expected to suit their intended purpose.
Such in-process meetings functionally serve to reduce anxiety on the part of the customer with regard to whether their money is being well spent, and on the part of the developer that their work will, when complete, be accepted and paid for. From both perspectives, they provide an opportunity to react to the vicissitudes of developmental fortune and other unexpected issues.
Contrast with Audit, with which there can be some process overlap.