Gemeindeverband is a generic term for several administrative subdivisions of Germany above the level of Gemeinde organized as a statutory corporation (Körperschaft des öffentlichen Rechts). The word is mentioned multiple times in the Grundgesetz, but without an exact definition.
Examples of what is commonly seen as a Gemeindeverband are:
At the level above Landkreis (commonly summarised as Höherer Kommunalverband):
At the level above Gemeinde and below Landkreis: