Energy Security is a term that describes the ability to protect access to fuels and electricity. Nations, businesses and families need the ability to generate or purchase fuels and electricity, either through imports or domestic production. They are reliant upon fuels or electricity consuming devices (vehicles, computers, factories, homes, etc) to carry out daily functions. They are dependent upon the ability to securely distribute fuels and transmit electricity to the right place, usually by boat, rail, truck, air, pipeline, or electrical grid.
The Department of Defense as an organization is the single largest consumer of fossil fuel in the world. A December 2005 'snowflake' by then Secretary of Defense Donald Rumsfeld asked what the DoD could do to reduce it's reliance on foreign oil, a large part of U.S. fuel consumption and electricity generation. As a result of the snowflake, an Energy Security Working Group was stood up under the Director for Defense Research and Development in April 2005 to analyze the issue.
The Energy Information Agency (part of the U.S. Department of Energy) has an [Energy Security Website] that provides up-to-date statistics and information on such topics as oil supply disruptions, domestic energy supply shortages, and events that affect energy security on a global basis.