What is the operating mode and role of a backup port on a shared LAN segment in Rapid PVST+?

A learning port is preparing to forward but not yet forwarding traffic, and a backup port's role is not to provide the shortest path; that is the role of a root port.

In Rapid PVST+, a backup port is a port on a designated bridge that is in a blocking state, providing an alternate path to the designated bridge for that segment. It is ready to transition quickly to a forwarding state if the designated port fails, offering faster convergence.

A forwarding port is actively sending/receiving traffic and is part of the active topology, whereas a backup port is explicitly in a blocking state.

Listening mode is an intermediate state in traditional STP; in Rapid PVST+, ports transition more quickly or are primarily in blocking/forwarding states, and while it provides an alternate path, its operating mode is blocking.