Dear lord, the misinformation in here...and after Droid803 gave you all the right answer to boot. Let's try this again, shall we?
INFR1 = Inferno Release 1. The original Inferno release. The Inferno release you can still download from the Inferno website. Includes a patch that makes it SCP-compatible.
INFR2 = Inferno Release 2. The sequel to the original Inferno release, which would have continued on its storyline after the GTVA/EA cease-fire. Now discontinued in favor of a new Inferno version.
INFA = Inferno: Alliance. A reasonably recent side-campaign detailing the creation of the Earth Alliance after the collapse of the Sol jump node. Will be deprecated by its upcoming stand-alone version.
INFASA = Inferno: Alliance Stand-Alone. An in-progress refurbished version of Inferno: Alliance with revised missions and storyline progression. Being stand-alone, it won't require that one have retail FS2 installed in order for it to run, much like The Babylon Project.
INFA2 = Inferno: Alliance 2. A planned sequel to Inferno: Alliance that will continue its story and presumably share its upcoming stand-alone nature.
INFSCP = Inferno: Source Code Project. The "main event" of the entire Inferno mod, in a manner of speaking. A complete revamping of the original Inferno release that will re-tell its story and continue on past its ending point into what would have been covered by R2. Will take advantage of SCP features in both mission design and mod content. Will also presumably be stand-alone, though don't quote me on that.
S:AH = Sol: A History. A relatively old campaign by Blaise Russell set in the Inferno universe and using its mods that tells the story of the Earth Alliance's development. Not considered part of Inferno canon, as it's a fan work.
(And all of this is why I hate overuse of acronyms...)