A president is the leader of a state (commonly called "country") or a division thereof, typically a republic, a democracy, or a dictatorship. The title "president" is sometimes used by extension for leaders of other groups, including corporate entities and social groups.
Etymologically, a is one who (from Latin prae- "before" + sedere "to sit"; giving the term praeses). Originally, the term referred to the presiding officer of a ceremony or meeting (i.e., chairman), but today it most commonly refers to an executive official. Among other things, "president" today is a common title for the heads of state of most republics, whether presidential republics, semi-presidential republics or parliamentary republics.
The title president is derived from the Latin prae- "before" + sedere "to sit." As such, it originally designated the officer who presides over or "sits before" a gathering and ensures that debate is conducted according to the rules of order (see also chairman and speaker). Early examples are from the universities of Oxford and Cambridge (from 1464) and the founding President of the Royal Society William Brouncker in 1660. This usage survives today in the title of such offices as "President of the Board of Trade" and "Lord President of the Council" in the United Kingdom, as well as "President of the Senate" (one of the roles constitutionally assigned to the Vice President of the United States). The officiating priest at certain Anglican religious services, too, is sometimes called the "president" in this sense. However, the most common modern usage is as the title of a head of state in a republic.