Augments are a enhancements to your character. There is a wide variety of augments available, including Melee Bonus, Additional Hit, Hurt Ethereal, Ignore Metal Defense, Absorb TP, Enhanse Utsusemi, Enhance Parry and so on.
There are three ways to receive an augment. First, most Ignition boosts will activate a temporary augment while the boost is on. Second, some pieces of armor will have augments always on while you're wearing the armor. Finally, weapons can have augments attached to them.
One way to augment a weapon is by using a rune. Once you have one you can use !augment add weapon rune. To remove an augment: !augment remove weapon. Remember that you cannot reclaim the rune by doing this.
Use the command !augment by itself to see the augments you have equipped, !augment list [player] to see all augments possessed.
The other way to augment a weapon is by reforging. This requires one repair hammer and black orbs equal to twice the cost of the weapon. Fists can't be reforged, but can be augmented using a rune. To reforge a weapon, enter !reforge weapon. The augment that you gain from reforging is completely random, but it's possible to get any augment in the game, including some that can't be obtained any other way (such as Absorb Ignition Gauge).