Causes a high amount of threat. Having your pet boar initiate a solo fight with Charge -> Growl will stick aggro to it to the point that it will take a lucky series of critical hits to pull the enemy off it. For Beastmastery hunters, the combination of Charge -> Growl -> Intimidation is a sure-fire way to pull that rogue monster off your cloth-wearers.
The boar turns red while under the Charge buff.
Charge shares its cooldown with Dash. To clarify, one cannot tell their boar to attack a target, and expect it first use Dash to get within 25 yards of the target, then use Charge the rest of the way.
At present, there is no mob which can teach Charge (Rank 4).