What is "gruppenkommandeur"

Gruppenkommandeur is a Luftwaffe position (not rank), that is the equivalent of a commander of a group or wing in other air forces. Gruppenkommandeur usually has the rank of Oberstleutnant (Lieutenant Colonel), and commands a Gruppe, which is a sub-division of a Geschwader. A Gruppe usually consists of three or four Staffeln, commanded by a Staffelkapitän.