The Vorpal Blade is a weapon found in the realm of Wonderland, and is said to be the only known weapon that is capable of killing the legendary Jabberwock. The blade was used against the Jabberwock long ago by an unknown hero, whom managed to incapacitate the beast rather then kill it, and was thus seen as a hero by the denizens of Wonderland.
The blade was later used by Alice, however, it is said that she has thought to been killed by the Jabberwock and the blade was lost for eternity. The Vorpal Blade is a weapon that is capable of killing creatures that manifest from a person's psyche. A Tulpa in particular fears this weapon, for they are artifical thought forms created from the minds of others.
It is loosely implied that the blade may have a will of its own, as the Cheshire Cat states it is "keen and always ready for service," personifying it and suggesting it has a desire to allow Alice, and others whom share the same sort of mental state as hers, wield it and/or be used in combat once again. It is also seen flying into Alice's hands when she first discovers it, meaning that it can act on its own accord. However, it is unknown if the blade can move on its own, or if another force was giving it to Alice.