I am confused about the title of leaders. For example, sometimes we call the top leader of a country 'president' or 'prime minister'. While sometimes I have heard 'chancellor' or some other titles. "

A loyal reader of bbcukchina.com

Every country has a head of state, or head of government. But not every country uses the same term of reference for its leader. The UK has a prime minister, the United States has a president, Germany has a chancellor, China has 国家主席 president 和国务院总理 premier.

So what does each of the above terms of address mean? What is the difference?

Neil and Li explain.