Tap

Tapped is a state that occurs when a player damages a mob, locking its experience gain, loot and corpse to be available only to that player or anyone in that player's party. Another term for a tap is a "tag". This state is indicated by the mob's health bar turning gray in the unit frame.

Most of the time and for most creatures, up to 5 non-grouped players can tap the same creature and will receive loot. That is, the creature will be no tap for those five players, then tapped for all others.

Trying to use an item or various crowd controls on a mob that has been tapped by someone else or someone from outside the player's party will return the error message "Target is tapped." However, players can still attack and kill the tapped mob even if they were not the ones to tap it. It is possible for one player to tap multiple mobs in order to keep others from doing so. Even if a mob is tapped, players will not get credit for the kill if most of the damage was caused by an NPC, or if all of the damage was caused by a permanent pet. Thus, low-level players can't get loot from high-level mobs by pulling them to guards, and pet classes can't use their pets to AFK grind.

For a quest where the objective is to kill a named mob, tapping will generally not prevent the quest objective from being marked complete for other players who dealt damage to it, even if those players cannot loot the corpse.

Players cannot be tapped. Whenever a player dies while in combat with another player, all nearby living enemy players of high enough level earn an honorable kill, even if they didn't participate in the fight and even if most of the damage was caused by a mob.

Shared tap
Specific mobs can have their taps shared between players, grouped or not, so long as they are in the same faction (Alliance or Horde). This is called "shared tap" or "tap-to-faction". In this case, each player is treated as having a concurrent tap on the mob. Thus, although the gold dropped by a mob will be split evenly between all players or groups who had a tap on the mob, most other drops are awarded to each player involved in the kill. There are exceptions for special items (like mounts), or for world bosses, in which case items are awarded using the personal loot system. Most shared tap mobs (outside of world bosses) will have their health scale in proportion to the number of players the mob is in combat with. This scaling has a limit of around five times the base health of the mob.

Examples of shared tap mobs include:
 * Quest bosses on Tol Barad Peninsula (and Problim)
 * Nearly all Pandaria world bosses (Sha of Anger, Galleon, Nalak, Oondasta, Celestial challenges)
 * Champions of Lei Shen on the Isle of Thunder
 * Krakkanon
 * Overburdened Laborers in the Northern Barrens

No tap
More recently, specific mobs were created in a no-tap state. All players of either faction who are in combat with a mob when it dies will get credit for the kill. The same rules for health scaling and loot distribution that shared-tap mobs follow apply to no-tap mobs as well.

No tap mobs include:
 * Kor'kron Commanders in Northern Barrens
 * Timeless Champions on Timeless Isle
 * Moonfang on Darkmoon Island