A DMZ (demilitarized zone) refers to a special network that can be accessed from the Internet as well as from the local network (LAN). A firewall completely blocks all access from the DMZ to the LAN. This concept allows you to make server services (such as e-mail servers) in the DMZ available for access from the Internet as well as from the LAN, but does not make you vulnerable to attacks on the LAN from the Internet.
FRITZ!Box does not support the implementation of a DMZ (demilitarized zone). Still there exist a workaround in the form of an exposed host.