I tried finding out what is the meaning of i in Oracle 9i, and g in oracle 10g, 11g. All I could find is 'i' in 9i is for Internet and 'g' in 10g, 11g, is for Grid computing.
Can someone please tell me what exactly does this mean? How oracle using Internet, grid computing and what are the benefits?
You missed that the newest version is 12c, with c standing for "cloud".
As @UweKeim says, this is largely a marketing gimmick. It's true Oracle did introduce functionality in those versions which were vaguely pertinent to the label. For instance, 8i built on the 8.0 ORDBMS paradigm and gave us Java Stored Procedures and embedded XML processing. 9i went further with its native XML capability, XMLType. However, these were just features which could be used in any database application.
Also, as far as grid computing goes, arguably Oracle's per socket / per core licensing policy militates against anything approaching genuine grid computing for all but the richest organisations.