Simple definition
Hyper-V Storage Migration moves a virtual machine's storage files to another location while the VM remains running.
Purpose and use
Hyper-V storage migration moves VM files to another supported storage location.
How does it work?
The VM can remain on the same host; affected files and migration capabilities depend on the scenario.
Example and verification
Verify destination paths, permissions, free capacity and VM state after the move.
Points to watch
Moving files is not a backup and does not necessarily move execution to another server.
In short
Storage migration and migration of the execution host are different operations.