http://wiki.guildwars.com/wiki/User:Vanguard
^If you scroll down to some headlines, I have an entire explanation on the birth of my username, starting from "Vanguard: The Term".
Edit:
Short version for those who can't handle walls of text;
Vanguard: NOUN: 1. The foremost position in an army or fleet advancing into battle. 2a. The foremost or leading position in a trend or movement. b. Those occupying a foremost position. ETYMOLOGY: Middle English vandgard, from avaunt garde, from Old French : avaunt, before (from Latin abante; see advance) + garde, guard (from garder, to guard; see guard). American Heritage Dictionary.
A vanguard is the forward element of an advancing military Tactical formation. Wikipedia.