Porcelain is just one of the types of ceramic tile. All ceramic (including porcelain) tile is made from clay mixed with sand and water. The clay itself is what makes all the difference. Clay containing high amounts of the mineral called “kaolinite” was and still is used in making porcelain tile. Kaolinite gives clay a very light colored appearance, and so the original porcelain meant quite literally “light colored clay”
Porcelain is also often described is a much denser material then ceramic. However the density is produced by firing the clay. The hotter and longer the clay is fired, the denser the tile is.
These days in the USA, the term porcelain tile has been simply converted in to describing a denser ceramic tile.
So there you have it:
If you see “porcelain” written on the box of tile, it just means that perhaps this tile was fired longer and hotter, and if it ANSI compliant it also means that it is water impervious.
One thing we have to remember, is that because of many years of misusing the term “porcelain” we all think that somehow ceramic tile is not as good as porcelain, but this is simply not true.