An executive order is a rule or order made by a President of the United States. The order tells agencies and officers of the Federal government of the United States things that they must do.
Executive orders can be stopped by the courts in a process called judicial review. They may be stopped if they are against laws or against the Constitution of the United States.
Executive orders have a big effect on the internal affairs of government. They decide how and to what degree legislation will be enforced. They also deal with emergencies and wars.