This category is for tablet PCs with either a single folding screen, or dual-screen devices with halves that fold together. They differ from slates in that they can fold, and differ from convertibles, in that there is no attached keyboard.
In dimension, they have a deceptively small in footprint, but when unfolded, can have screens that rival large laptops. For example, the X1 Fold is 12" when folded, but has a 16.3" screen when unfolded.
This combination of large screen productivity and small notebook portability is what sets this device category apart from all other tablets.