I have been following the boys since their pre-debut days and that's the first time I'm hearing of this. I'm pretty sure that only stands for NCT DREAM.
NCT's concept was basically infinite amount of members with infinite amounts of units. Members from different units could collaborate and make a new unit for themselves or they could form an entire new unit with completely new members. There's just no limit to anything. It was originally also meant to be that members could just leave any unit whenever they liked too but I doubt it's as easy as it sounds.
Right now, NCT U is the experimental (?) unit, or the unit where different members can get together and collaborate and whatever else. SM seems to have made that change which makes sense since it would probably be too messy to have a hundred different units when you can just have one dedicated to collabs between members from different units.
NCT 127 was originally supposed to be the fixed Korean unit but I have no idea what SM is planning to do with that since they keep adding (Johnny, Doyoung & Jungwoo) and removing (Win Win) members. There were rumours that the 127 boys would be the leaders of other units in the future (Yuta for J-unit, Win Win for C unit, Mark for Dream, Johnny for US unit etc.) but that doesn't look like it's happening. But I think the current 127 members will be the final line-up, with maybe Yuta being sent to the J-unit in the future. I don't think they'll add in anymore.
As for Dream, well that was the unit that was meant to be rotational since their concept is the fresh teenage boys concept. It would be weird to have adult boys with that concept. So the current members will graduate once they're older and debut in different units in the future and new younger members will replace them. I don't think the graduating boys will be 127 so either they'll release music under U or SM will go along with the original concept and debut more units. But that said, I think from now on SM might only debut the Korean trainees in DREAM first. The foreign ones will debut in different countries. I don't think there will be another new unit debuting anytime soon with new members. At most, we'll get one for the members that have graduated from DREAM.
WayV is basically the Chinese version of 127. I think if any members are removed, it would be TEN since SM said they wanted a SEA unit in the future and Renjun and Chenle might be added once they graduate from DREAM.
So DREAM aside, no other unit has that concept. But honestly, I don't think even SM knows what they're doing anymore. They changed the original plan so many times already and they'll only change it again later. They don't really seem to have a clear concept anymore so it seems they're just going with whatever works.