Guest Frame Numbers/Page Frame Numbers
In a virtualized environment, an additional or secondary translation is performed from the physical address as understood by the VM, or pseudo-physical address, to the real physical address of memory in the host, or machine address. This translation also uses a page table-like data structure. Frames of guest pseudo-physical memory are identified by Guest Frame Numbers (GFNs) while frames of machine real-physical memory are identified with Page Frame Numbers (PFNs). A skilled person would understand that the guest OS executing inside the VM still believes it is managing PFNs, and that the GFN/PFN distinction is only relevant in the context of the host virtualization software, e.g. VMM or hypervisors.
https://en.wikipedia.org/wiki/Second_Level_Address_Translation
https://revers.engineering/mmu-ept-technical-details/