Main Difference
The main difference between President and Chancellor is that the President is a leader of a country or part of a country, usually in republics and Chancellor is a position.
President
The president is a common title for the head of state in most republics. In politics, president is a title given to leaders of republican states.
The functions exercised by a president vary according to the form of government. In parliamentary republics, they are limited to those of the head of state, and are thus largely ceremonial. In presidential and semi-presidential republics, the role of the president is more prominent, encompassing also (in most cases) the functions of the head of government. In authoritarian regimes, a dictator or leader of a one-party state may also be called a president.
Chancellor
Chancellor (Latin: cancellarius) is a title of various official positions in the governments of many nations. The original chancellors were the cancellarii of Roman courts of justice—ushers, who sat at the cancelli or lattice work screens of a basilica or law court, which separated the judge and counsel from the audience. A chancellor’s office is called a chancellery or chancery. The word is now used in the titles of many various officers in all kinds of settings (government, education, religion). Nowadays the term is most often used to describe:
The head of the government
A person in charge of foreign affairs
A person with duties related to justice
A person in charge of financial and economic issues
The head of a university
President (noun)
The head of state of a republic, a representative democracy and sometimes a dictatorship.
“The vast majority of presidents have been male.”
President (noun)
Primary leader of a corporation. Not to be confused with CEO, which is a related but separate position that is sometimes held by a different person.
President (noun)
A person presiding over a meeting, chair, presiding officer, presider.
President (noun)
obsolete form of precedent
President (adjective)
Occupying the first rank or chief place; having the highest authority; presiding.
Chancellor (noun)
A senior official with duties, sometimes finance or justice.
“Chancellor of the Duchy of Lancaster”
“Lord Chancellor”
Chancellor (noun)
The head of the government in some German-countries.
“Reichskanzler|q1=historical”
“the Austrian Chancellor”
Chancellor (noun)
A senior cases involving ecclesiastical law.
Chancellor (noun)
The head of a ceremonial.
Chancellor (noun)
The foreman of a jury.
Chancellor (noun)
The chief judge of a court of exercising equity jurisdiction).