In an ongoing series of posts about various aspects of the rules, I'm revisiting the "You Call That A Knife?" entry. As I've been told, and as my research has shown me, the various categories of bladed weapons are pretty tough to pin down. However, this is not a treatise on the history of swords but a look at the game rules. It is almost ridiculously simplistic but one would do well to keep in mind D&D is, after all, a game. If one has an interest in real life medieval swords, the Oakeshott's Typology of The Medieval Sword is an excellent starting point for your research (my thanks to Wayne Rossi for the link).
Dagger: a short and relatively light one-handed weapon. Daggers are typically double-edged and are allowed in all but the most restrictive of societies. Often worn concealed.
Short Sword: a short one-handed weapon, worn openly. Lighter and faster than longswords, short swords are favored melee weapons for missile troops and thieves. The latter often use a main gauche, or parrying dagger, in tandem with the short sword.
Long Sword: the longest bladed weapon intended solely for use with one hand and often used in tandem with a shield or, less typically in this era, a main gauche.
Bastard Sword: longer than a long sword, the bastard or "hand-and-a-half" sword can be wielded one- or two-handed. Typically used one-handed by stronger fighters, and as a two-hander by weaker humans and man-types of shorter stature.
Two-Handed Sword: a very long bladed weapon intended for two-handed use by full-size humans of no less than average strength and more often by stronger than average fighters.
Variations on bladed weapons include one-edged, two-edged, pointed, curved inward, and curved outward variations. The endari (High Elves) on Khordesh favor a long sword with an extended hilt, basically making it a smaller bastard sword. Thieves and Scouts use a main gauche instead of a shield, which grants a shield +1 bonus to AC against one melee opponent and is of no effect versus missile fire. We are still considering allowing the main gauche variant of sword breaker into our milieu. This would allow the wielder a free attack in certain conditions.