The longsword or long sword is a bladed melee weapon common in nearly any medieval or fantasy setting. The longsword is typically characterized by a long, straight double-edged blade and a cruciform hilt. The blade typically ends in a point, making it effective for both slashing and thrusting. They are also referred to as "broadswords" (though that designation can depend on the historical period or setting).
Though the typical game-and-fantasy "longsword" is a single-handed weapon, the true historical equivalent is closer to the "arming sword" (or "knightly sword") of the High Medieval era. The historical "longsword" is actually the "bastard sword" of the same period, having a hilt long enough to account for two-handed use. Longswords and arming swords eventually became the common sidearm of the medieval era, evolving into the cut-and-thrust swords of the Renaissance period.
A useful general definition for defining a fantasy or game longsword would be "a European/Medieval sword that's longer than a short sword and shorter than a greatsword." That's not a very sophisticated description, to be sure, but it accurately reflects the weapon's place in most fictional settings.
Contrary to popular belief, longswords had their own codified and advanced forms of fighting, that included single-handed wielding, grips with one hand on the pommel, half-swording (one hand on the blade), and the use of the pommel and cross as a striking weapon.
Usage in Games
The longsword is one of the most ubiquitous weapons in medieval fiction, a near-necessity for any setting, alongside the bow-and-arrow or axe.
In the Dungeons & Dragons
3rd Edition ruleset, the basic damage for a longsword-class weapon is "1d8", standing for one roll of an eight-sided die, with a minimum of 1 and maximum of 8 damage (not counting modifiers). The 4th Edition rules have eliminate the "1", leaving the amount of die rolls dependent upon the power being used at the time.
Longswords fall into the basic "Bladed" skill category in The Elder Scrolls 4: Oblivion
Noted longswords include the talking weapon Enserric of Neverwinter Nights: Hordes of the Underdark
(though Enserric could technically transform into any weapon the player chose), Blackrazor of Baldur's Gate II: Shadows of Amn
, which was a reward for the player's giving in to greed during a test of morality, and Umbra
incarnation was a two-handed claymore).