They are often translated as "municipality".
In the English language, a municipality often is defined as relating to a single city or town; however, in Spanish, the term "municipio" may not mean a single city or town, but rather a jurisdiction housing several towns and cities, like a township, county, borough or civil parish.
The Italian term "municipalità" refers either to a single city or a group of cities and towns in a township, but the Portugal's use is almost entirely restricted to group of cities or towns like in a county, township and so forth.
However, in Brazil, a Municipio is an independent city & a public corporporation with status of Federated Entity.
Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Municipio.