The Elder Wand, variably known as the Deathstick, the Wand of Destiny, the Eldruhn Wand and the Elhorn Wand, is one of the Deathly Hallows. According to legend, whoever unites it with the Resurrection Stone and the Cloak of Invisibility will be the Master of Death. It is said to be the most powerful wand that has ever existed, and is able to perform feats of magic that would normally be considered impossible. For example, it was able to fully repair another damaged wand and allow it to function normally after it had been broken.
[EDIT] Like other wands only the true master can perform the wand's full potential. For example, when Voldemort used very powerful magic, the wand started to crack, because the wand wasn't truely his and was performing very powerful magic.