* Headmaster: Traditionally used for the head of a boys' school.
* Headmistress: Traditionally used for the head of a girls' school.
* Headteacher: A gender-neutral term commonly used in the UK.
* Principal: A common term in the US and many other countries.
* Head of School: A more general term, often used in independent or private schools.
* President: Sometimes used in universities or colleges, and sometimes in some private schools.
* Chancellor: Often found in universities, but sometimes in other institutions.
The best term to use will depend on context.