(OPerations SECurity) The U.S. military term for concealing critical information as part of a counterintelligence plan. A form of "security by obscurity," OPSEC determines what information adversaries can obtain or piece together from observation and to provide measures for reducing such vulnerabilities to acceptable levels. An informative report entitled the Joint Doctrine for Information Operations is available at www.dtic.mil/doctrine/jel/new_pubs/jp3_13.pdf. See security by obscurity.