Protected VLANs are all other VLANs that are members of the STPD.
These VLANs “piggyback” on the carrier VLAN. Protected VLANs do not transmit or receive STP BPDUs, but they are affected by STP state changes and inherit the state of the carrier VLAN. Protected VLANs can participate in multiple STPDs, but any particular port in the VLAN can belong to only one STPD. Also known as non-carrier VLANs.
If you configure MSTP, all member VLANs in an MSTP region are protected VLANs. These VLANs do not transmit or receive STP BPDUs, but they are affected by STP state changes communicated by the CIST to the MSTP regions. Multiple spanning tree instances (MSTIs) cannot share the same protected VLAN; however, any port in a protected VLAN can belong to multiple MSTIs. For more information about MSTP, see Multiple Spanning Tree Protocol.