ACN91 is fuel, Arizona, California, Nevada, 91 octane. It's fuel specifically in these states. From what I've gathered around the forums, it pales in comparison to 91 from other states. Exactly why, I can't say. I'd assume it has to do with additives relating to emission standards but that's just speculation.
Stage 1 is a level of modification done to the vehicle, essentially from stock to very minor power modifications. The map, in this case, is a number of set parameters that reprogram the ECU for the given mods (in this case, I believe just better electronic engine management--tuning).
tl;dr=tuning the stock vehicle for 91 octane in AZ,CA,NV.