Or mirror unit.

Mit Spiegelreferat werden die den politischen Abteilungen untergeordneten Referate im Bundeskanzleramt bezeichnet. Die Bezeichnung leitet sich davon ab, dass jedes dieser Referate einem Referat in einem Fachministerium entspricht (dieses spiegelt). Aufgabe der Spiegelreferate ist es die Arbeit der entsprechenden Referate in den Fachministerien zu begleiten und so den Bundeskanzler in die Lage zu versetzen die Arbeit dieser kompetent zu verfolgen.
http://www.lexexakt.de/glossar/spiegelreferat.php

The Chancellery deals with departmental affairs in parallel with the Ministries. As the structure of the Chancellery’s working units mirrors this, they are also known as the ‘mirror divisions’.

The task of these mirror divisions is to either be informed on all essential affairs in their respective field or to ensure being updated as quickly as possible. The mirror divisions fulfil what might be called a liaison role between the respective departments on the one hand and the Chancellor and the Chancellery on the other.

http://www.bundeskanzlerin.de/Webs/BK/En/Angela-Merkel/Tasks...

The policy units of the Chancellor’s Office are either ´mirror-units´ (Spiegelreferate) which are responsible for the policy field of a single ministry, or >cross-sectional units< (Querschnittsreferate), whose responsibilities cut across several ministries. An example of the former is unit No. 312, named >Ministry of Public Health<; an example of the latter is unit No. 131 dealing with the relationship between the federation and the Laender.

http://www.karlheinz-niclauss.de/chancellor.htm