An Operational Evaluation (OPEVAL), the final phase of operational test and evaluation prior to fielding of a system or new equipment, is a process used by NATO military forces and designed to be no more than a 'customer acceptance' test. OPEVALs are run by the customer's agent, in the military's case one of the operational test agencies (OTAs) and uses a pre-designated operationally oriented test plan. The intent of the test is to verify that the product or proposed system meets all pre-defined operational requirements.

OPEVALs are widely associated with STANAG

STANAG

STANAG is the NATO abbreviation for Standardization Agreement, which sets up processes, procedures, terms, and conditions for common military or technical procedures or equipment between the member countries of the alliance. Each NATO state ratifies a STANAG and implements it within their own...

requirements and documentation.