What is the backup port in spanning tree?In which scenario we will be able to see a backup port role on a swichport?

Switch 1 will send BPDU from port 0/1 & 0/2. But Switch 2 will receive the BPDU transmitted from 0/1 of Switch because that port is elected as DP forwarding. The port 0/2 on Switch 1 is backup port because it will transition as DP forwarding in case if port 0/1 on switch 1 is no longer active.

In conclusion, a port which provides backup to DP port is called Backup port.

backup port are the next secondary path towards to reach next switch. in other way we can say backup up port is the another option of designated port.when designated port fail then backup port will take place as a new designated port.