The porcelain on the right (Plainsman Polar Ice), breaks much more like glass, to razor sharp-knife edges. But it is not a glass, it is a zero-porosity, dense matrix of glass-bonded crystals. The whiteware on the left (Plainsman M370) has 1% porosity, and although vitreous and quite strong, clearly it is not in the same class as the one on the right.
The term vitrified refers to the fired state of a piece of porcelain or stoneware. Vitrified ware has been fired high enough to make it very strong, hard and dense.