Yorkie

vitreous means the material has an extremely low permeability to liquids.Ceramic wall tiles usually have a higher water absorbtion anywhere upto 15% they are then glazed to make them impervious. Without getting to technicalVitrified means glass has formed in the ceramic and really all ceramics are vitrified to some degree so it is not really a good term. "Fully Vitrfied" or porcelain tiles would have a water absorption rate of <0.5% and are therfore impervious without the need for glaze. Tiles with higher water absorption rates (say <6.0%) are at times refered to as "Vitrified" they would most likely be glazed and be designed for use on floors.