A short sword, is a small blade that is longer than a dagger or dirk but shorter a longsword. It is, in essence, a smaller version of the longsword, having many of the same parts including a generally double-edged blade, crossguard, handle, and pommel.
Shortswords are standard issue to many different types of soldiers. Archers favor this weapon for use when the range shortens to such a point that their bows are no longer effective and many warriors, including Fighters, Barbarians, Paladins, and Rangers carry these weapons as a secondary if not a primary for use in the off-hand. Light and maneuverable, yet able to provide many different types of attacks, it is arguably the most common weapon on the battlefield. Shortswords generally have blades ranging from 12 to 20 in. (30.4 to 50.8 cm). The weapon is light enough to be finessable but its smaller nature means it deals less damage than a heavier blade. In two-weapon fighting styles, the short sword is often not the primary weapon but instead a complimentary weapon to a larger blade.
Shortswords are common throughout all parts of Toril, including but not limited to Faerun, Kara-Tur, and Zakhara. As usual, depending upon what part of Toril you're standing in, they are known by different colloquial names. In Faerun in addition to being known as a shortsword you may also hear the terms gladius or warsword. In the eastern lands of Kara-Tur they can be found by the names of wakizashi or the exotic butterfly sword. Finally, in the areas of Zakhara they may be referred to as falcata or bast.