Associated states

An associated state is the minor partner in a formal, free relationship between a political territory with a degree of statehood and a (usually larger) nation, for which no other specific term, such as protectorate, is adopted. The details of such free association are contained in United Nations General Assembly resolution 1541 (XV) Principle VI, a Compact of Free Association or Associated Statehood Act and are specific to the countries involved. In the case of the Cook Islands and Niue, the details of their free association arrangement are contained in several documents, such as their respective constitutions, the 1983 Exchange of Letters between the governments of New Zealand and the Cook Islands, and the 2001 Joint Centenary Declaration. Free associated states can be described as independent or not, but free association is not a qualification of an entity's statehood or status as a subject of international law.

Informally it can be considered more widely: from a post-colonial form of amical protection, or protectorate, to confederation of unequal members when the lesser partner(s) delegate(s) to the major one (often the former colonial power) some authority normally exclusively retained by a sovereign state, usually in such fields as defense and foreign relations, while often enjoying favorable economic terms such as market access.

According to some scholars, a form of association based on benign protection and delegation of sovereignty can be seen as a defining feature of microstates.

A federacy, a type of government where at least one of the subunits in an otherwise unitary state enjoys autonomy like a subunit within a federation, is similar to an associated state, with such subunit(s) having considerable independence in internal issues, except foreign affairs and defence. Yet in terms of international law it is a completely different situation because the subunits are not independent international entities and have no potential right to independence.

...
Wikipedia