In VLAN aware switches, internally all VLANs are tagged.
On an ethernet port carrying multiple VLANs, you can chose a single VLAN to be untagged on that port.
That's what PVID configures. (In Cisco terminology , it's called the native VLAN)
It's common to have VLAN1 untagged, but that's not mandatory.
Configuring PVID=10 and VID=1,2,3,4 uses untagged packets for VLAN10, and VLAN1...4 are tagged . Yes, VLAN1 tagged!