The name is a reference to the famed mythical sword, Excalibur. Excalibur was said to have been given to King Arthur by the Lady of the Lake; upon Arthur's death, the sword was returned to her. (There are some variations on how King Arthur acquired the sword, but this version is more correct - inasmuch as a myth can be "correct.")
For characters not wielding an heirloom weapon, this is a nice sword. Lots of strength, good stamina, and an excellent speed. The appearance is nice to look at, as well.
"Post constructively or I'll press some different buttons next time." -- CM Daeleht (from the old WoW website, no source link)