Taunt is a disable that forces one or more units to attack another unit.
A taunt forces the affected unit to drop any of its current order, and start attacking the taunting unit instead. This means it fully cancels attack orders against other units, ability cast orders and channeling spells. If the taunted unit is out of attack range, it moves towards the taunt source until within attack range. The unit only uses regular movement to get closer to the taunting unit, it does not utilize abilities to close the gap. The Fog of War does not prevent the unit from losing track of the taunting unit, but invisibility does.
A taunted unit is still subject to every other disable. The taunt does not make them ignore disarms or movement imparing effects. If a taunted unit is disarmed, it follows the taunting unit, so that they stay within attack range. They continue attacking as soon as the disarm expires.
While taunted, a unit can be given orders, which it then executes as soon as the taunt ends, similar to how an order get queued up when given while stunned. If no order is given, the unit continues to auto-attack nearby enemies, regardless of auto-attack settings, until a new order is given. Due to this, shift-queueing an order while taunt queues it after the auto-attack, so that the unit will execute the queued order once it stops attacking. Therefore, in order to shift-queue while taunted, the first order must be given without SHIFT.
It is impossible for a unit to attack multiple targets at the same time, therefore, there are some priority rules. Generally, when hit by multiple sources of taunt, the unit attacks whoever taunted them first. Once the first taunt expires, they immediately switch to the second source, if it is still active. The exception to this is Duel, which always takes priority over other taunts.
Taunts also do not stack with Fear, which has a similar concept to taunt, forcing units to flee towards their fountain (or their camps, in case of neutral creeps). When stacked with these, Taunt takes priority. Taunting a unit affected by Fear makes them move towards the taunt source. Applying Fear on a unit affected by Taunt does not make them flee. However, since Fear completely prevents the unit from acting, it cannot attack the taunting unit, and therefore only follows it until able to attack again. The unit continues, or starts fleeing as soon as the taunt ends, if the Fear did not expire by then.
Taunts are very similar to stuns, as they prevent the unit from doing almost anything. As such, it can be used to completely stop an enemy, protect allies, initiate and interrupt channeling spells by disrupting the enemy. Its advantage of stuns is that it can also be used to displace enemies, especially melee units. Taunted units still must be within attack range to attack the taunt source, so that they have to move closer when out of range. Depending on how long the taunt lasts, this can be used to force enemies out of position.
Since taunts force units to attack, it can be used to break most sources of invisibility which break upon attacking. It can also make units waste single-use or charge-based attack modifier on unintended, like the Shadow Realm attack or Refraction charges.
Sources of taunt