A proxy board is a requirement imposed under a Proxy Agreement by the U.S. Department of Defense's Defense Security Service on foreign investors seeking to acquire certain American companies. This is for national security reasons and applies mainly to defense contractors which are involved in highly classified contracts. The Proxy Agreement is between the foreign company, the US subsidiary holding classified contracts and the DSS.
A proxy board is a board composed entirely of American citizens which are responsible for the day-to-day running of the business. In this way the company's classified information is "insulated" from foreign exploitation but the parent company still benefits from any profits made by its subsidiary.