It's my understanding that "Butters, Buttering" is first a generic term for flatland tricks when riding the board in a "Pressed" position either nose or tail.
That said, a straight butter, is simply riding straight, reg or switch while pressing the board. (...nose or tail slightly raised,)
Nose/Tail rolls, are when you are adding rotation to your press and swinging around 180 degrees on the nose or tail of the board. Additionally, you can add ollies, nollies, and other variations of moves to make them even more Steezy!
. You can either be riding a straight press and then rotate around, or you can start your rotation while riding flat and then raise your nose or tail for the nose rolls!
Then of course,... Just to add to you confusion! You can do them Front side, Back side, reg, switch, etc, etc.
In general tho, the term Butters is / can be used generically for mist all of them.
Jeb,(...as Snowmie.com) as well as Snowboardaddiction.com has video showing and describing most of those variations of buttering moves.
Hope that helps! Good Luck!