Q: What is Hyper-V Replica Trust Group?
A. When configuring Hyper-V to accept replica information from servers, one of the options is to configure a Trust Group value. This value (which is really just a tag) is designed to control which servers can replicate between each other.
Imagine you have virtual machines (VMs) that move between hosts. Provided those hosts have the same trust group defined, the VM can move between them, but replication using Hyper-V Replica would continue.
It can also be useful in a host-type environment to ensure one client can't send deltas for VMs to another client's VMs. This can be configured in the GUI but also can be done by using Windows PowerShell: