Porcelain tiles are typically made with "porcelain" clays that have specific properties. Typically, these tiles are dense and by definition, they have water absorption of 0.5% or less. Non-porcelain tiles have water absorption greater than 0.5%.
Because porcelain tiles have a low water absorption, they are usually frost resistant, although, not always. To know if a tile is frost resistant, you should check the manufacturer's literature. There are also many non-porcelain tiles that can be used in freeze thaw environments and that are manufactured with properties similar to porcelain tiles.
There are both glazed and unglazed porcelain tiles. It is important to know the difference, as the glazed variety is usually a little easier to clean. Typically, glazed porcelain tiles have filled in microscopic holes that could be present in the unglazed tile. On the other hand, unglazed porcelains may have better slip resistance.
Non-porcelain tiles cover a wide range of properties. Typically they are glazed (unglazed quarry tile is the exception), and the glaze layer can be extremely durable. However, as there are differences from one glaze to another, it is important to check if the tile has been tested and to make sure the glaze hardness is suitable for your application.
In general, non-porcelain tiles are easier to bond to the floor and usually easier to cut. Porcelain tiles are harder to bond and harder to cut. While this can be relevant to the tile installer, it generally makes little difference to the end-user, so long as the installer uses the right materials.

Some people refer to unglazed porcelain tile as "through body" ( i.e., the color on the top goes all the way through). Even in extreme applications, these tiles tend not to show wear as the porcelain is quite durable (harder than granite), and the color goes all the way through. Many glazed porcelains also have extremely good durability. Although the color in the glaze layer may be different from the body, the surface is usually sufficiently resistant to abrasion to not show wear in typical applications.

When a tile is "rectified" its edges are cut at the factory after it is baked. The natural, pressed and somewhat rounded edges of the tile are cut and machined to produce a fairly sharp, precise edge with a micro-bevel and a flat surface at the perimeter. This procedure is common for porcelain floor tile but is also sometimes performed on large format ceramic wall tiles. With this precision the tiles can be set with a 2 mm to 3 mm grout joint and due to the flatness at the edges the joints are less visible.

No. Wall tiles have a weaker glaze and body and will wear prematurely. It is also not as resistant to impact and stress when used as a floor finish and may spall, chip and crack. However, a floor tile can definitely be used on walls.

Today, most floor tiles on the market are porcelain. A porcelain tile is essentially a ceramic tile in the architectural world, that is, there are two classifications of ceramic tiles, porcelain and non-porcelain. The latest styles and designs are only manufactured as porcelain products. Porcelain floor tiles have a more dense body and, typically, harder glazes than ceramic floor tiles. In its manufacture, higher temperatures and finer clays are used and an extra mineral component is added to make it a porcelain tile.

This is a highly polished porcelain tile, usually rectified, that is produced by applying a thick glaze, machining it smooth and polishing it. Glazes are necessary for printing broad digital inkjet designs onto the tile. Unglazed porcelain, which can also be highly polished, is not suitable for most digital inkjet designs.

Unglazed porcelain tiles are highly polished and have rectified edges. They are usually through-body porcelain and suitable for commercial traffic. Some of them are treated with an impregnating sealer at the factory whereas others may have a label on the carton that states that a solvent-based impregnator needs to be applied during installation.

To be used outdoors, the tile must be frost proof, unglazed and have a highly textured surface for slip resistance. Make sure the absorption rate is 0.5% or less. (This will differ depending on the climate and weather patterns of your location.)

Ceramic tile is constructed using red, brown or white clay. Porcelain tile, however, is constructed using white clay. As a result of being made from more refined clay, porcelain tiles are more durable, making them ideal for harsher applications such as commercial or outdoor flooring. Also, because of their higher density, porcelain tiles are less likely to absorb moisture (0.5%), making them more durable and resistant to staining. Porcelain tiles are frequently found in floor applications, outdoor areas and in cold weather climates where freezing can occur. With their low absorption capability they are less likely to crack in cold weather climates. Porcelain tile costs a little more than the traditional, more porous, standard clay tile. However, prices have been coming down in recent years.

The finish on different semi-polished tiles can vary from a very slight polish on the high spots of a textured glaze to an almost fully polished surface that reveals some pits or dull areas. Often it is done to more authentically duplicate stone tile which have some natural fissures. It is also less slippery and less susceptible to visible scratches than fully polished tiles.