Definition:
Management by crisis is a phrase used to describe the common problem of allowing unexpected events, interruptions, problems, or emergencies to dictate your priorities and actions.
Effective crisis management is an important best practice; it is an essential skill of effective time managers because unexpected things do happen in every project. Sometimes we do need to react quickly to a crisis and contain it before it does more damage. The problem comes when crisis management becomes the routine rather than the exception. If you spend more of your time putting out fires than doing your work, you are managing by crisis.
Further Reading:
Book: The Unified modeling Language user guide by Grady Booch, James Rumbaugh and Ivar Jacobson