A think tank (or policy institute) is an organization that conducts research and engages in advocacy in areas such as social policy, political strategy, economy, science or technology issues, industrial or business policies, or military advice.
Many think tanks are non-profit organizations, which some countries such as the United States and Canada provide with tax exempt status. Other think tanks are funded by governments, advocacy groups, or businesses, or derive revenue from consulting or research work related to their projects.
 See The American Heritage Dictionary. "Think Tank." 2000. and Merriam Webster's Dictionary. "Think Tank."
 Diane Stone 'Think Tanks and Policy Analysis', in Frank Fischer, Gerald J. Miller. & Mara S. Sidney (eds.) Handbook of Public Policy Analysis: Theory, Methods, and Politics, New York, Marcel Dekker Inc. 2006: 149-157