Train has a few meanings in World of Warcraft and MMORPGs:
- To improve some ability, power, or skill by paying a Trainer or reading a training Book.
- To use aggro to draw a bunch of mobs so they attack another group of Player characters.
- To have several players use the auto-follow feature to travel in a long line.
- The silly emote: /train
How Do I Train A Skill?
Find a trainer for the skill you want or want to improve and pay them the required money for the new ability, power, recipe, spell or skill.
Trainers can usually be found in larger settlements, such as towns or cities, but they are scattered throughout the world. The easiest way to find most trainers is to talk to a guard in a capital city.
Training Mobs
See also: Kite, aggro dump, Monster Player Kill
In an MMORPG, it is often possible to grief another player or party by aggroing a number of nearby mobs that would ordinarily not be close enough to see the target party, then running toward the party so that the mobs chase you into them and attack them. If done at an inopportune moment, such as when the other player or party is currently fighting a close fight, this can turn their victory into a defeat and possibly a party wipe, making "training" a way for a single player to use the environment to defeat an entire party of the opposite faction – or even of the same faction.
The developers of World of Warcraft seem to have realized that this is undesirable – even on a PvP server, the fact that one player could successfully and repeatedly grief an entire party of other players, even players of the same faction, could have a strong negative impact on a lot of people's gaming experiences. The WoW developers aren't against grieving behavior when there's a PvP remedy (if you can get together a group of allies to trounce the offending party or simply kill all the mobs quickly, the problem is solved), but when the griever is impossible to attack (is not set PvP, or is of the same faction as his targets), there is no such PvP remedy. There are, therefore, countermeasures against mob training in WoW:
- Outside of instances, a mob will break off pursuit of a player that stops attacking it, unless that player remains close to the mob spawn point. Once the mob is a sufficient distance from where it started, a player attempting to train it must continually attack it in some way, or else it will leash back to its spawn point in Evade mode, ignoring everything until it gets there. Inside instances things are different - mobs will typically chase players until they catch them.
- A mob that is targeting a player will keep targeting that one until another player moves to the top of its aggro list for some reason – the targeted player can die,
[Vanish], use 
[Feign Death], etc., or another player can do enough damage to the mob to supplant the first player at the top of the mob's list. If there is no one else on its list, the mob leashes back to its spawn point, again meaning that it ignores everything on the way back.
- Inside a normal (non-heroic/non-raid) instance, the only players present are all in the same party, so there is no way for a player not in the party/group to train mobs on them.
- It's possible to have multiple parties in the same heroic/raid instances, provided that all the party leaders have the same Raid ID. This can occurs under two circumstances: (1) the instance was not completed and more than one person decided to resume it, or (2) someone, having the Raid ID, decides to grief people and remain in the instance (which would take away an available spot in the instance so no one can get in).
It is therefore difficult to train mobs on anybody in WoW; they will only attack the target party if someone in the target party (although this does include hunter and warlock pets) hits the mob as it goes by, and then only if the would-be mob trainer dies rather than getting away. If the mob trainer escapes, even if the mob has somebody else on its aggro list, the mob(s) will just leash back to their spawn points, ignoring the target party, and reset.
Training mobs on somebody has been made very difficult in WoW, although it is still not totally impossible. If done in such a way that there is no PvP remedy to the situation, it is a reportable offense.
One of the most famous examples of training occurred when a Horde guild successfully pulled Kazzak to Stormwind.
Train Emote
- When a player types in /train, they will start making train noises and movements. "Woo wooooo! Chugga chugga chugga..."