PVID = Port Vlan ID
PVID (Port VLAN ID) is a default VLAN id assigned to frames coming to the port

Example 1.

interface fa0/1
  switchport mode access
  switchport access vlan 10
  switchport voice vlan 20
  switchport trunk native vlan 30

Here PVID is 10, as untagged frames will get into VLAN 10.

Example 2

interface fa0/2
  switchport mode trunk
  switchport access vlan 10
  switchport voice vlan 20
  switchport trunk native vlan 30

Here PVID is 30, as untagged frames will get into VLAN 30.