Porcelain

Porcelain tiles are a form of ceramic tiles.

Whilst the preparation of ceramic and porcelain tiles are similar, it is the pressing and firing process which results in the porcelain tile having the superior characteristics of being much stronger and less porous, generally with a water absorption rate of 0.5% or less.What are the types of porcelain Tiles?

Polished or Semi Polished: as the name suggests, an elaborate technique is used to finish the tile after the firing process. High quality porcelain does not require any further treatment after polishing. 
Some lower density polished porcelain tiles must be sealed, depending on the manufacturer.
 A polished surface is not a glaze, so do not be fooled into thinking that polished porcelain is glazed.

Glazed Porcelain: various techniques are employed by different manufacturers to glaze a tile. Once a porcelain tile has been glazed, no further treatment is required, in the sense that these tiles are considered non porous.

Matt, Honed or Natural Porcelain: generally speaking, this type of product comes out of the kiln in this form and undergoes no further processing. 
A quality product requires no further treatment, ie. normally sealing is not required.

Rock Finish or Structured Porcelain: this type of porcelain is extremely textured and often used for external purposes. Normally sealing is not required.