A state of emergency is a situation in which a government is empowered to perform actions that it would normally not be permitted. A government can declare such state during a disaster, civil unrest, or armed conflict. Such declaration alerts citizens to change their normal behavior and orders government agencies to implement emergency plans. Justitium is its equivalent in Roman law—a concept in which the senate could put forward a final decree (senatus consultum ultimum) that was not subject to dispute.
States of emergency can also be used as a rationale or pretext for suspending rights and freedoms guaranteed under a country's constitution or basic law. The procedure for and legality of doing so vary by country. Wikipedia