Tertiary government usually refers to the lowest organizational level of government

Government

Government refers to the legislators, administrators, and arbitrators in the administrative bureaucracy who control a state at a given time, and to the system of government by which they are organized...

 within three-layered federal

Federation

A federation , also known as a federal state, is a type of sovereign state characterized by a union of partially self-governing states or regions united by a central government...

 systems. Typical federal systems include:

1. the principal national government
   Central government
   A central government also known as a national government, union government and in federal states, the federal government, is the government at the level of the nation-state. The structure of central governments varies from institution to institution...
   
   ;
2. the secondary province
   Province
   A province is a territorial unit, almost always an administrative division, within a country or state.-Etymology:The English word "province" is attested since about 1330 and derives from the 13th-century Old French "province," which itself comes from the Latin word "provincia," which referred to...
   
   s, states or departments
   Department (subnational entity)
   Department is the name given to the administrative and political subdivisions of many countries.As a territorial unit, "department" was first used by the French Revolutionary governments, apparently to emphasize that each territory was simply an administrative sub-division of the united sovereign...
   
   ; and,
3. the tertiary municipalities
   Municipality
   A municipality is essentially an urban administrative division having corporate status and usually powers of self-government. It can also be used to mean the governing body of a municipality. A municipality is a general-purpose administrative subdivision, as opposed to a special-purpose district...
   
   , counties
   County
   A county is a jurisdiction of local government in certain modern nations. Historically in mainland Europe, the original French term, comté, and its equivalents in other languages denoted a jurisdiction under the sovereignty of a count A county is a jurisdiction of local government in certain...
   
    or townships.

This generalization glosses over "microrregional" organizations of greater cities

Metropolitan area

The term metropolitan area refers to a region consisting of a densely populated urban core and its less-populated surrounding territories, sharing industry, infrastructure, and housing. A metropolitan area usually encompasses multiple jurisdictions and municipalities: neighborhoods, townships,...

 and associations of counties or municipalities. It also does not take into account intergovernmental or supranational levels of governance, such as the European Union

European Union

The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...

, the United Nations

United Nations

The United Nations is an international organization whose stated aims are facilitating cooperation in international law, international security, economic development, social progress, human rights, and achievement of world peace...

, or the World Trade Organization

World Trade Organization

The World Trade Organization is an organization that intends to supervise and liberalize international trade. The organization officially commenced on January 1, 1995 under the Marrakech Agreement, replacing the General Agreement on Tariffs and Trade , which commenced in 1948...

for example.