That basically means that in IP subnet your machine in, you have available free IP address which will be consumed by emulator network support when you configure it in its settings. This dedicated IP will raise up as secondary IP on ethernet interface whereas primary IP remains in use by OS networking stack.
In case of DHCP you may wish to ensure that DHCP server in your segment would grant additional IP address for your ethernet interface.
This all is because emulator ethernet support does not overlay IP address used by OS, but assumes dedicated IP address. Ethernet interface may have more than one IP address assigned, so that single machine may represent several hosts. In case of emulator support Operation System acts as primary network host, while emulator appears as standalone additional host, hence the requirement for dedicated IP.