Wikipedia
Reichskommissariat is the German designation for a type of administrative office headed by a government official known as a Reichskommissar . Although many different such offices existed primarily throughout the Imperial German and Nazi periods in a number of different fields (such as public infrastructure, spatial planning, ethnic cleansing, etc.) it is most commonly used to refer to the quasi-colonial territorial units established by Nazi Germany in several occupied countries during World War II. While officially located outside of the German Reich in a legal sense, these entities were directly controlled by their supreme civil authorities (the Reichskommissars), who ruled their assigned territories as German governors on behalf of and as direct representatives of Adolf Hitler.
The introduction of these territorial administrations served a number of purposes. Those established or planned to be established in Western and Northern Europe were in general envisioned as the transitional phases for the future incorporation of various Germanic countries outside of pre-war Germany into an expanded Nazi state. Their eastern counterparts served primarily colonialist and imperialist purposes, as sources of future Lebensraum for German settlement and the exploitation of natural resources.
Another contrast was the level of administrative overhaul implemented in these two types. As in most other territories conquered by the Germans, local administrators and bureaucrats were pressured to continue their regular day-to-day operations (especially at the middle and lower levels) albeit under German oversight. Throughout the war the Reichskommissariate in Western and Northern Europe simply retained the previously existing administrative structure however, while in the eastern ones completely new such structures were introduced.
All of these entities were nonetheless intended for eventual integration into a Greater Germanic Reich encompassing the general area of Europe stretching from the North Sea to the Ural mountains, for which Germany was to form the basis.