An executive order or executive decree is a rule or order, or a law made by a head of state (president or monarch) who has this power given to him by the constitution of the country. The order tells ministries, agencies, the civil service and the military of a state the things that they must do.
Executive orders can be stopped by the courts in a process called judicial review. They may be stopped by the courts or the legislature if they are against laws or against the constitution.
However, in countries where there is no real separation of powers and the head of state is actually a dictator, the executive order cannot be stopped by the courts or the legislature, which as a result have no powers and are controlled by him. In many cases, the head of state with dictatorial powers often rules the country by making executive orders rather than making laws in the legislature which he also controls.
Executive orders have a big effect on the internal affairs of the government and on the citizens. They decide how and to what degree legislation will be enforced. They also deal with emergencies and wars.