Here you go:
http://en.wikipedia.org/wiki/State_of_Emergency"A state of emergency is a governmental declaration that may suspend certain normal functions of government, may work to alert citizens to alter their normal behaviors, or may order government agencies to implement emergency preparedness plans. It can also be used as a rationale for suspending civil liberties. Such declarations usually come during a time of natural disaster, during periods of civil unrest, or following a declaration of war (therefore, in democratic countries many call this martial law, most with non critical intent)."
Specifically:
A federal emergency declaration allows the Federal Emergency Management Agency (FEMA) to exercise its power to deal with emergency situations; federal assistance also become available to areas that are declared to be in a state of emergency. For FEMA, emergency declarations are different from the more common disaster declarations done for hurricanes and floods.
http://en.wikipedia.org/wiki/State_of_Emergency#The_United_StatesRead more. It is "martial law lite".