A president is the highest head of state in most republics. He/she could be a full-fledged chief of government or just a ceremonial figurehead, depending on the constitution and culture of each country.
In the United States, the president heads a complex network of Federal departments and independent agencies with missions and responsibilities as broad as appointing justices to the Supreme Court to deciding whether to use American troops abroad. The president is also the leader on the world stage, negotiating with other nations and shaping international affairs.
A president’s executive branch powers include directing other departments and granting pardons. As commander-in-chief of the armed forces, the president oversees military actions. The president also appoints department and agency heads who are responsible for enforcing and administering Federal laws. In addition to appointing members of the Supreme Court, he/she may also appoint judges to lower courts like district and appeals courts.
The president is required to take the expert advice of Attorney General and chief justice before executing their judicial duties. They are also able to prevent unconstitutional activities of parliament/state legislatures and union cabinet by refusing compulsory assent/government orders.
The term can also be used to describe the head of a sub-national entity such as the parish presidents in the U.S. state of Louisiana, the borough presidents of New York City, or the municipal presidents in Mexico’s municipalities. However, this usage of the term is not as widely recognised as the parliamentary and presidential use.