Balthazar's Faction

The Battle Isles includes many arenas where you can earn faction. Both Tyria (in Prophecies) and Cantha (in Factions) have competitive arenas as well.
Many beginning players start to earn faction in the Random and Team Arenas of the Battle Isles.
Others start in low-level arenas in the cooperative side of the game, such as the Old Ascalon Arena (in Prophecies) or the Shing Jea Arena (in Factions); you cannot play with a character above 10th level in either of those locations.

As an example of faction rewards, those four arenas (Random, Team, Old Ascalon, and Shing Jea) give the same rewards for PvP conflict. You can earn Balthazar's faction by killing another PvP character (that is, earning 20 faction for reducing an enemy character's Health to 0) or by winning a match (earning 25 faction for defeating another team). If nobody on your team dies, it's a Flawless Victory, and each character earns additional 25 faction.

After you find a Priest of Balthazar in the Battle Isles, you can trade the faction you've earned for skills and runes useable only in PvP. http://www.guildwars.com/gameplay/exploring/titlesandfactions.php