This specifies the numbered access-list (0-100) that defines which multicast group address range is served by this Rendezvous Point, per its description, with 0 meaning no access-list restriction applies. It lets an admin scope a PIM Rendezvous Point to only a subset of multicast groups rather than making it responsible for the entire multicast address space, which matters for load distribution across multiple RPs in a network. Setting this to access-list 10, which might permit only 239.1.1.0/24, means this RP only handles rendezvous for that specific group range while other RPs cover the rest.