UPnP is a collection of protocols which allow devices to discover and communicate with each other. Miniupnpd supports the UPnP Internet Gateway Device (IGD) specifications and allows devices and apps (games consoles/TiVo/Torrent Clients/PC games/etc to set up port forwarding on the gateway automatically. It is a common function in domestic routers and Miniupnpd is ClearOS's implementation of it.
The underlying miniupnpd package is maintained by the MiniUPnP Project
This currently only has a Start/Stop button.
The app will automatically detect your default WAN interface and all your LAN (not HotLAN or DMZ) interfaces and configure itself to use them.
If you want to enable it for your HotLAN, please uncomment the line in /etc/miniupnpd/miniupnpd_clearos.conf.
All other configurations options are found in /etc/miniupnpd/miniupnpd.conf