Hi,
a port VLAN ID is the assigned VLAN of an access-port.
The native VLAN is used in a trunk. A trunk is used to connect another switch or a device which belongs to more than 1 VLAN. Since a standard ethernet frame doesn't provide a field to distinguish VLANs, a special field is inserted, this is called "tagging". Nevertheless, frames belonging to the native VLAN are transmitted without such a tag (in other words: the ethernet frames are not modified). In this way, traffic forwaring is possible in the native VLAN even when the trunk is not working correctly.
In theory, when you would connect a trunkport from one switch to an accessport of another, communication for the native VLAN would be possible. In such a scenario, the native VLAN-ID doesn't have to match the PVID. Hope, this isn't to confusing.
You can find more details in discussion https://learningnetwork.cisco.com/thread/8721#39225
Regards,
Rolf
