Why the bridge0 has a Ethernet port address? it refers to what?

what's the ether 82:13:08:b0:ec:c0 meaning? is it a MAC address? as we know a Ethernet port should have one. but why the bridge0 have one? is it refers to a Ethernet port of it, but which?

First, the device bridge0 simultaneously represents two things: the actual L2 bridge and a virtual Ethernet port that connects the host OS itself to that bridge.

Individual bridge/switch ports generally do not have their own MAC addresses, but devices connected to them do. So in this case, 82:13:08:b0:ec:c0 is the MAC address of the host OS connected to the bridge. If bridge0 had an IP address, the OS would send the IP packets using that MAC address.

But also note that even when bridges/switches don't need to speak IP, they are still not completely passive devices on the network: they often use STP (Spanning Tree Protocol) to interact with other bridges on the network for avoiding loops, so each STP-speaking bridge of course needs its own MAC address for the STP packets. (The "Configuration:" subsection of your ifconfig output consists entirely of STP-related parameters; the 'id' is blank because STP is disabled.)

So 82:13:08:b0:ec:c0 is the bridge's MAC address when it speaks STP. (More advanced "enterprise" switches might also speak LLDP, 802.1X, and various other link-layer protocols that require the switch to have its own MAC address.) Although again, technically it's the bridge's host OS that does this – connected to the bridge through an internal port (this is true even on physical Ethernet switches; they have a so-called "CPU port").

It seems from your output that you're running macOS, or at least some BSD-like OS. If that is the case, don't mind much the comments about "ifconfig being obsolete" – while they are very true on Linux (where the 'ip' and 'bridge' tools are preferred), none of it applies to the BSDs.

1. Yes that is a MAC address. A bridge interface acts like a virtual ethernet interface, so it needs the same characteristics as one.

2. Yes. (I note the tool you are using is not really appropriate for dealing with details of beidges, and has been deprecated).