They don't actually stand for anything, the name was originally written: eGo, as in e-Go or i-Go (the trend to write an e- or i- in front of something to make it sound digital or modern or whatever. It's just a Go with an e- prefix.
Janty designed the eGo and originally had it manufactured by Joyetech in China. It was similar to the penstyles that filled that slot originally, but designed to be a better replacement. The penstyles had the advantage of the best atty made up to that date (the 801) but as they used the 3-piece system, leaks and other glitches were common. The eGo introduced the mid-size or fat-batt class of ecigs to the market. That made it a three tier market for hardware as it still is today: minis (now often called cigalikes), mid-size (the eGo's etc), and APVs (mods).
The kGo is basically the same but with an 801 connector, IIRC.
Janty didn't realise how big the eGo market would go and didn't bother to trademark or patent the name or design. That was about a $100 million mistake and ranks as one of the biggest ever screw-ups in the ecig world.
Janty and Joyetech quality are very good compared to the rest of the market. The knock-offs aren't normally as good, and some of the hundreds of el cheapo copies are very poor in comparison. In particular, clone eGo's and chargers have the worst record for fires while being charged of any ecig product.