A cabinet department or prime minister's department is a department or other government agency that directly supports the work of the government's central executive office, usually the cabinet and/or prime minister, rather than specific ministerial portfolios.
The department is roughly equivalent in function to a president's office in a presidential system of government or an office of the council of ministers in a semi-presidential system.
In many countries, such a department is called a Prime Minister's Office.
In the United Kingdom, the Prime Minister's Office is a part of the Cabinet Office; in Australia and New Zealand, there is a single department called the Department of the Prime Minister and Cabinet.
In some countries, such as Germany and Poland, the department supporting the prime minister (the Chancellor in Germany) is called the chancellery.