It is the vis required to be reported prior to the ABP in order to continue the approach PAST the ABP.
There are no visual reference requirements after that in a CatIIIb (no DH) approach.
Other low vis approaches have different visual reference requirements at minima (e.g, Cat IIIa requires three center-line lights), but that is different from needing to determine that a particular RVR is available after the ABP.