The term has no definite meaning I'm aware of. However, it is reasonable to apply it to those who think the Confederacy was in the right.
Now it is theoretically possible for a modern person to think the CSA was right only in its desire for state sovereignty, without bringing along all the white supremacist stuff usually associated with support for the Confederacy. Recognizing that white supremacy was an almost universally held POV by white people in the 1860s. North and South.
Unfortunately that's not really the way it works out. While northern racists (most northerners) didn't want to live around or have anything to do with blacks, the dominant southern ideology was a very definite Master Race ideology, and we all know where that tends to lead over time. IOW, southern racism insisted blacks be forever enslaved for the benefit of their white masters, while northern racism wished blacks would just go away.
While neither POV is admirable or defensible by modern standards, northern racism was at least willing to leave other races alone.
Mechanization would eventually have done away with the need for slaves, and without bankrupting the Southern agrarian economy. I highly doubt that ANYONE -- North or South -- "insisted blacks be forever enslaved for the benefit of their white masters."
I personally believe that the Confederacy WAS in the right as far as the state sovereignty question is concerned. And while I freely admit to being a racist, since I do not beg forgiveness from black people for sins I've never committed, I do not see myself as a White Supremacist, nor do I align myself with that ideology, which I regard as laughably stupid.
And for what it's worth, I am from an area about as far north of the Mason-Dixon as you can get.