Gajanan,
I have heard/read several versions of 'what S4HANA' stands for but most believable:
HANA = High-performance ANalytic Appliance (although some state that HANA is a proper noun & not an acronym)
S4 = comes from the fact that it is the 4th generation of SAP Business Suite
hence
SAP Business Suite 4 (generation) for SAP High-performance ANalytic Appliance = SAP S4 HANA.
It is stated that it's development involved (among other things) rewriting 400 million lines of code and does not require batch processing.
And since you mentioned - it is much more "Real Time" that R/3 or any other ERP product of matching scale.
I think it is a very exciting product launched by SAP and with all the new architecture it can also be called HAsso's New Architecture (another popular side story about HANA's acronym)
[Hasso Plattner - Cofounder of SAP AG]
Regards
Shivraj Singh