Excalibur is the strongest sword in the game (except for the Tizona in the Console Version) and is part of the hallowed weaponry set. Excalibur can continuously attack, which can be useful for charging into a group of enemies. Like all of the Hallowed weapons, Excalibur gives off a faint glow and emits a sparkle effect along with sound when swung.
While swinging this item, you cannot turn around but you can "Moonwalk" (walk backwards while swinging), similar to the War Axe of the Night, The Breaker, and several other items.
In the Underground Hallow, there exists a Enemy called Enchanted Sword which looks exactly like this.
The sword's name comes from Arthurian legend, in which Excalibur is the sword of King Arthur with supposed magical properties, which is either pulled from (an anvil on) a stone or given to him by the Lady of the Lake.
Excalibur is said to be the holy sword of the gods. This is reinforced by the fact that the sword in-game is a Hallowed weapon.
In the economical sense, making and selling copies of Excalibur is not a viable method to make money, as Souls of Might are worth 2 a piece (With a full 20 being needed to make the sword - full value of 40 ), whereas the sword is only worth 4 60 . That's a profit loss of 88.5% on the Souls alone, which is quite considerable.