DMZ means, forward everything, FTP included.
In fact DMZ means: bypass and just forward everything. DMZ is used in case port forwarding still can't forward the protocol or port and you need to debug to see if this is really the case. You don't want to disable your entire firewall, so DMZ is used to forward everything to a specific ip address. DMZ stands for De-Militarized Zone. DMZ is also used if there are 2 or more routers in place, and you don't want to duplicate the router rules from one router to the other. DMZ on the first router forwards all traffic to the second router.
Basically the router works like this:
If traffic is incoming to a certain port, if there is a portforwarding rule, that rule is followed. If there isn't, the request is ignored. By enabling DMZ, this changes to: first do portforwarding rules, if there is no match, just forward the request to the DMZ.
A third option is called bridging. In case a router is set to bridge mode, it will disable the NAT translating all together. No portforwarding rules, no firewall, nothing. Everything gets forwarded directly to whatever is on the first lan port. This usually also means, that the other lan ports and wifi are disabled. This is useful if it is a modem/router combo and you only want to use the modem.