RSTP defined new 4 port roles:-
1. Root Port (Old One)
2. Designated Port (Old One)
3. Alternate Port (New One)
4. Backup Port (New One)
Alternate Port:- The alternate port is the port blocked by superior BPDU from a different bridge.
Backup Port:- The backup port is the port blocked by the BPDU sent from the same switch.