The discovered hosts page is a part of the host discovery plugin and will only exist if this plugin is installed on your orcharhino.
The discovered hosts page can be accessed via the hosts menu:
Hosts > Discovered hosts
The discovered hosts page lists discovered hosts before they are provisioned using orcharhino. Discovered hosts are hosts that were not created via orcharhino but where discovered using the discovery plugin for subsequent provisioning via orcharhino.
Refer to the host discovery guide for more information.