Honor system

The honor system is a way for players to gain honor rewards by participating in PvP (random, world or battleground). Additionally there are PvP Tokens earned in specific zones when killing players of the opposing faction:
 * Mark of Honor Hold - earned in Hellfire Peninsula and Zangarmarsh for Alliance Players.
 * Mark of Thrallmar - earned in Hellfire Peninsula and Zangarmarsh for Horde Players.
 * Halaa Battle Token - earned when killing players surrounding Halaa in Nagrand

Official Info
Patch 2.0 Honor System Changes at the official site:
 * What is the new player-versus-player (PvP) honor system?
 * Like the current PvP honor system, the new honor system provides a way for players to participate in PvP combat and obtain rewards by defeating their opponents. The key difference in the new honor system is how the rewards are obtained. With the new honor system, you will obtain honor points that can be accumulated and spent like currency on rewards such as items, weapons, and armor.


 * Do I need to keep playing to keep my honor points intact?
 * No, the honor points will accumulate like currency, similar to the gold and silver you can obtain through killing monsters or completing quests, and will not degrade or be lost over time. This allows you to participate in PvP at your own pace, working toward the honor rewards, which you can purchase as soon as you have enough honor points to do so. There is no longer any ranking associated with the honor system, so you no longer have to worry about maintaining a rank or standing under the honor system. Players still interested in measuring their PvP ability against fellow players will be able to participate in the Arena System, which is a separate, new form of competitive PvP in The Burning Crusade.


 * Is there a limit to how many honor points I can accumulate?
 * Yes, there is a limit to how many honor points a character can accumulate, but it is currently set to be approximately twice as much as the most expensive reward. If you max out your honor points, you'll need to spend some before you can earn additional honor points.


 * The limit of course, is subject to change depending on what works best for long-term game balance.


 * Are honor points the only thing needed to purchase the rewards?
 * The battleground marks of honor currently awarded for participating in Warsong Gulch, Arathi Basin, Alterac Valley, and Eye of the Storm will also factor in to the cost for many of the rewards. The amount of honor points and marks of honor required will vary for each reward. However, for most items the honor cost is the most significant part of the item's cost. As of patch 3.3m marks are no longer given out nor needed to make purchases. Existing marks may be converted into Honor Points.


 * Will the honor and battleground reputation rewards available in the current system still be available?
 * All of the same rewards are available in the new honor system, costing both honor points and marks of honor from the appropriate battleground.


 * What will happen to my current battleground reputations, honor, and rank?
 * A new title system will display your highest rank achieved under the old honor system, but ranks will no longer play a part in the new honor system. The battleground reputations will carry over to the new system, and still be visible and increase through participation in the various battlegrounds, but the current rewards are now only available through the new honor system. However, you will be able to obtain a special title if you obtain exalted reputation with each battleground faction. This title may be displayed through the new title display system.


 * What is the Honor System?
 * The Honor System allows players to gain Honor Points based on PvP kills and battles that can be used to spend on special rewards. Players earn Honor Points mainly through Battlegrounds and World Outdoor PvP. For more competitive battles, participate in the Arena System.


 * Once I gain Honor Points, do I keep it indefinitely, or do I have to keep earning it?
 * You keep them until you spend them. There is a limit to how many honor points a character can accumulate, but it is currently set to be approximately twice as much as the most expensive reward. If you max out your honor points, you'll need to spend some before you can earn additional honor points.

Legion
World of Warcraft: Legion will see extensive changes to PvP, including a new honor system.