A blade is the flat part of a bladed tool or weapon that (usually) has a cutting edge and/or pointed end typically made of a metal, such as Steel used to cut, stab, slice, throw, thrust, or strike.
Various techniques were also employed to make the blade harder. Copper and bronze can be "work-hardened" (or annealed) by simply hitting the blade with a hammer while it is cold. Blades made of Steel with a high enough Carbon content (greater than 0.2%) could be heat-treated by heating the steel up to a critical point (most alloys become non-magnetic at that point), then quenching it in water. Quenching puts an enormous amount of strain on the metal, and oftentimes a sword would break into pieces during that step. If the sword survived heat-treating, it would be tempered by heating it to a relatively low temperature for an extended period of time. The tempering process would make it slightly softer, but also tougher and "springier", and thus less likely to break or chip during the rigors of Combat.
Case-hardening is a process of increasing the carbon content at the surface of very low Carbon Steel. It is done by placing the object to be hardened in a sealed container along with carbon-containing material; in antiquity, this material was usually horn or hide. The container would then be heated until it was glowing red, and held at that temperature for awhile, based on the size of the part being hardened, allowing carbon to penetrate the steel by a few thousandths of a centimeter. At that point, the object would be dumped out of the container into a water bath to quench it, resulting in a very hard surface, but completely unhardened core. There is very little evidence of this having ever been done to swords except, perhaps, the very earliest of Iron blades.
Another important aspect of many blades are so-called "fullers". Despite popular belief, fullers were not "blood groves" that facilitated quicker bleeding of the victim. Rather fullers helped to make a blade lighter while still retaining much of its strength. They were made by positioning a heated blade over a bottom fuller, setting a like sized top fuller on the top side of the sword, and hitting the top fuller with a Hammer.
For a horseman, stabbing was not practical because it is hard to make a Horse move swiftly backward should the thrust fail to strike the victim. The cavalryman would then be at the mercy of his erstwhile victim. This was not so important in massed Cavalry charges, in any case in such attacks the cavalry would often be in closely packed formations in which slashing would not be possible. Consequently, European heavy cavalry generally had straight swords.
Cavalry that engaged in single combat or in looser formations normally had curved swords. In order to cut, a sword had to be drawn across the victim's skin, and a curved sword was more suitable for this. The blade was only sharpened on the outer edge and the RADIUS of curvature was equal to the distance from the centre about which the blade was rotated - i.e. the distance from the blade to the shoulder.
In curved European swords, this was usually a full arm's length, but in the Middle East and Indian swords it as generally a much shorter distance - typically 50 cm or so (see Scimitar). This gave Eastern cavalry a great advantage over their European counterparts because they were able to fight at a closer distance than the Europeans were used to and therefore get inside their sword arc.
Single-edged swords have a back. This is the unsharpened edge. Early 19th century swords had a "pipe-backed" appearance, whereby they had a thickened ridge along the back to make the blade stronger.