A copy of the OS, on the sdcard. Takes space, can be modified and launched from there, but your system partition (nand) stays clean. (Unless you make it dirty for no reason (looks at TX)).
True, but sysnand will have no traces of your emunand activities. If you are not TX and put some personaly coded files there. (TX, we think for our users - so they dont have to, and get banned...). So those are two separate environments. Think of it as rooms. One room you pirate in, the other one you dont.
Thing is, Nintedo might detect (online) all rooms they didn't build.
(So dont go online with emunand, but with sysnand and you are fine. At which point you'd have to decide - do I want "online" (sysnand has to be most current firmware), or do I want "chance of dongle free in the future" - in which case, sysnand stays on any low firmware you want to stay on. (no online)
With the TX' OS you get neither one of those options.
They say "because there is no interest in the broader public" - what they really mean though is - "our customers are too stupid to do complex things". So we give them piracy, say - you will accept bans - and to only use our solution from now on. And now please hand over the money in the extasy fuled vodoo orgies, that gbatemp threads with "sale link here - I bought! piracy!" threads usually are.)
TLDR; All the dumb people go with TX, and then can't complain to any of the bright people in the future. But they can ask TX for "service" - because they now have TX DRMed Switches, son.