A treasurer is someone who looks after the money in a club, company, organization, association, or government.
The treasurer of a government manages the Annual Budget of a state or country. The budget is used to give money to government departments and to pay for the debts or promises the government makes. This post is called Chancellor of the Exchequer in the United Kingdom. There is a treasurer of the United States, but the United States Secretary of the Treasury actually controls the department.