Again, GIS = 'geographic information system'. This term isn't very descriptive, however: OK, so this software does something with information that is georeferenced...does it draw bar graphs? Pie charts? Create scatterplots?
For this topic, I think showing is better than telling, so I'll explain through looking at a file in two different environments. First, take a look at the following Google Earth file: http://www.cwoodcock.com/Civil_War_by_Campaign.kmz
As you can tell, it's a Google Earth file, but I'll be moving it into a GIS after we look at it in Google Earth. You can download it to your computer, open it up in Google Earth, and then browse the file.
And here is the same file, plugged into a lightweight, online GIS environment (Esri's ArcGIS online): http://arcg.is/1CPHCyY
So: Is GIS just the same thing as Google Earth? How is it different? Do we care about the differences?