Tangs.
A tang is the method used to attach the blade to the handle.
Full tang is where the blade runs the full length of the sword and the handle is literally bolted onto the blade. These are incredibly strong and you will find almost all functional/battle intended pieces will have a full tang.
Rat-tail tang is where the blade comes to a stop just inside the handle, it's then welded onto a circluar piece of metal which runs the remaining length of the handle. Rat-tail is only used in decorative or ornamental pieces due to the fact it's incredibly weak.
Half/push tang is where the blade is pushed halfway into the handle and fixed in place. It's strong but not functional, it's mostly used for strong decorative pieces.
Common sword materials.
Folded carbon steel, originally the point of folding was to spread the carbon content out evenly along the blade and remove impurities, otherwise you would have soft and hard spots and the blade would easily break in these places. Modern steel is of a lot better quality and already has an evenly distributed carbon content, so there isn't really any need for folding to improve the strength of the blade (If it's forged correctly). Folded steel is just as strong as normal steel but in my view you can't beat the look of a well folded blade.
Carbon Steel is simply the toughest stuff you can get and it most likely won't come cheap. It's extremely important if you buy a carbon steel blade that you keep it protected from ther air (oil will provide a good cover for the blade) as it will oxidise rust if left in contact with oxygen. There are various different 'styles' of carbon steel. The best being High Spring Carbon Steel and Damascus Carbon Steel
440 C is a stainless steel and a very robust metal, this is used in some of the cheaper functional/battle intended blades and in several of the decorative/ornamental pieces.
420 J2 this is top quality stainless steel, it's a precision metal and can be incredibly well polished, also it won't rust or stain. It's often refered to as 'surgical steel' because it's the same metal used for surgical equipment.
Strength/hardness of carbon steel.
The strength/hardness of steel is measured by units called "Rockwell's" on a scale known as the Rockwell C scale (RC). The higher the Rockwell value the stronger/harder the metal is, the higher the number dosn't always relate to the quality of the blade. Some blades need to be flexible and have different properties and many are made of more than one strength of steel such as forged and folded blades.
30-40 RC. This level of strength/hardness is the lowest RC you allow for a sword. Swords repeatedly exposed to edge-on-edge fighting will dent but not chip and can be hammered back straight at 40 rc.
40-45 RC. This is a good RC to be used on the spine of differentially heat-treated swords. This hardness level will have some spring qualities, allowing the blade to flex slightly and therefore absorb the impact of the collision.
50-52 RC. This is the most common for the European and medieval style blades. A blade of this rc will give you a good middle-line between hardness for holding an edge and strength. It's still soft enough to be a good shock absorber though, dampening vibrations passed through the blade to the tang then to your hands.
58-60 RC. This is the ideal strength/hardness for the edge of differently heat treated blades like Japanese katanas and Chinese swords. A blade with an edge of this hardness can slice into most materials that are comparably softer like some woods and plastics.
Well that's all I've got for now,but there is one last thing. To quickly explain my rage towards the comments quoted earlier. A sword shouldn't be razor sharp. The fantasy that how well a sword cuts is purely based on how sharp it, is one that is widespread among novices and movies. Skill, practice, balance and training are what determines how well a sword will cut. The functional swords are sharpened to exact degree they need to be for their intended purpose. To razor sharpen a blade will take it to such a fine edge that it will be brittle and prone to chipping, particularly when you consider the forces involved when a blade swung at full force will come under when it meets it's target. Even a sword that does not feel very sharp will still perform well, a good example to show this is to hold a piece of A4 paper and watch the blade slice this neatly in half.
If you read all of this then thank you and please leave a comment.