K4NT is actually a pleonasm, as all K4 models are "non-touch".
It stems from the time when the Kindle 4 and Kindle Touch were released, and *both* of them were referred to as "K4" ("Touch" and "Non-Touch) - even if that's obviously wrong, because the Touch is a K5.
And for some reason, many people just stuck to calling it the "K4NT" instead of just "K4".
BTW, You'll occasionally see "K4S" and "K4B" as well - standing for "silver" (the old model) and "black" (the new model). In terms of software/hacking, these should be pretty much identical.
PS: The version numbers we use come directly from the device info dialog. So, in that numbering scheme, both the Touch and Paperwhite are K5*, and the Kindle Fires would be K6 (and K7?).
(*) That's actually a bit unfortunate. So people tend to be explicit when speaking about the Paperwhite ("PW"/"KPW"/"KP").