From Wikipedia entry on Burzum:

"The choice of the name for the project reflects both this influence and the desire for anonymity: "Burzum" is a word of the Black Speech of Mordor meaning "darkness" (though Vikernes believes that Pagans consider it to mean "light" as opposed to how Christians consider it to mean "darkness"), and is one of those found on the Ring-inscription of the One Ring (the final part of the Ring inscription being "...agh Burzum-ishi krimpatul", "...and in the darkness bind them")."