Actually #4 is the technical (or original) sniping, whereas the above 3 are splitting a train.
Sniping is when you retake a village very quickly after someone new nobles it, and splitting (what the majority now call sniping), is when you stick support troops or returning troops inbetween nobles.
Also, I can already see people arguing with me over what sniping is and splitting is. Originally players really didn't know how to split trains under a second, or at least not many did back in the day, so it wasn't such a popular strategy, and sniping was considered grabbing a village off of a player just after they nobled it. This could be sniping a village back, or sniping a village you just saw was nobled, etc. Fairly self explanatory. People argue with me constantly about this, just know that I am right.
I started playing .net just 2-3 months after it opened, so I would know.