'Intaglio' is to me the same thing as 'cavo relievo' (also 'cavo rilievo') though you will find others differentiating these and the minutiae of other relief carving terms. Essentially, the surrounding wood is untouched and the relief carving is sunk below.
This way of carving is very quick way because you don't need to spend time removing all that background. You can see this style in many Egyptian wall carvings and elsewhere on Woodcarving Workshops.tv. For example:
The main thing is to establish a strong outline before you carve within...