The HARM targeting system is a pod mounted to the side of an F-16 aircraft that enables the aircraft to track the location of hostile radar systems that can then be engaged with AGM-88 HARM or other air-to-surface weapons.
US Air Force HARM Targeting Pod Page: http://www.af.mil/AboutUs/FactSheets/Display/tabid/224/Article/104602/high-speed-anti-radiation-missile-targeting-system.aspx