Although it is only GM jiberish, it can mean whatever you want it to.
Some guys have stated, Super Sport Edition inducted or Super Special Edition inducted or Super Sexy Edition inducted. In the older models you could order an SSE with a supercharged option but it didn't change it to an SSEi, the badge still said SSE.
When the new 2000'* first came out and I bought mine, I was in Anaheim California at a GM exhibition. There was a video display set up with all the marketing fan fare.
It stated that it meant Security, Safety, Efficiency, intelligence....and went on to list all the special features relating to each of those words that the SSEi has over its competition. I was impressed.