A unitary authority is a local authority responsible for all local government functions within its area or performing additional functions that elsewhere are usually performed by a higher level of sub-national government or the national government. Wikipedia

A type of local authority that has a single tier and is responsible for all local government functions within its area, or performs additional functions which elsewhere in the relevant country are usually performed by national government or a higher level of sub-national government Wikipedia Disambiguation

Local government body that covers two levels of government Wikidata

In local government, a single-tier authority which replaces a two-tier structure. For example, in England, county councils are abolished and their responsibilities are transferred to boroughs and local government districts (but this only applies to some counties, not all). In some cases complete counties, such as Cornwall and Northumberland, are now unitary authorities without any subdivision into local government districts. Wiktionary

A single-tier local government system. Wiktionary (translation)