This read-only MacAddr identifies a MAC address the switch has automatically detected as a duplicate, meaning two or more devices are claiming the same source address, and per the description, all frames using this address as their source are actively being discarded at the ports listed in ciscoTsDupAddrFilterPorts. This is an automatic protective mechanism rather than an admin-configured filter, so seeing an entry here at all indicates a real network misconfiguration, like a cloned NIC or misconfigured virtual MAC, that needs to be tracked down. An admin would use this MAC address to physically locate the offending duplicate device, since the switch is actively blocking it rather than just logging it.