The word has evolved to describe a person who:
* Presides over a meeting or organization: This is the most basic meaning. For example, the president of a club leads the meetings and sets the agenda.
* Heads a state or government: This is the most common meaning in modern usage. The president of a country is the highest-ranking official and often has executive power.
* Heads a company or organization: This meaning is similar to the previous one, but refers to the leader of a private entity.
Therefore, the word "president" fundamentally conveys the idea of leadership and authority.