Government Accountability Office. The arm of Congress that investigates the performance of the federal government. GAO evaluates the use of public funds and the performance of federal programs, while also providing analytical, investigative and legal services in order to support to Congress in its policy formulation and decision making processes. Most GAO reports are initiated at the request of Congress, while some are initiated by the agency itself or are required by law. Until 2004, GAO stood for General Accounting Office.