I don't see a lot of point in defining the term "gank." I personally believe that if you remove someone's ability to fight back, you remove their chance to have fun as a player. I apply this to hugely lopsided teams, sniping, land mines and other similar tactics...
I don't force this on other people, but I do my best not to remove the other player's ability to fight back. If they don't have fun, even being enemies, then they won't want to play. I've seen games go extinct that way.
