Furball -- close range firefight. Derivation: originally, a military aviation term for a group of planes in a mutual dogfight. In HG:L, you often get into situations where you are being attacked by multiple attackers at a variety of ranges, including some melee attackers. In these situations, you generally don't want to be taking your targeting reticle off your current target in order to throw a grenade; the odds of hitting are too low and the time it takes to perform the action too long relative to the amount of damage the grenade is capable of doing. It's much easier to target with grenades accurately if you are not simultaneously having to evade enemy attacks, whereas dodging whilst shooting with a gun is much more natural.
Aggro -- Common MMORPG term (picked up from Guild Wars) for enemy aggression, that is, which PC the enemy monsters (mobs) are targeting. For instance, a guardian might precede other PCs into a room and perhaps use taunts to ensure that all the enemies are attacking him, since he's more capable of surviving such an onslaught than his allies are. This is called 'grabbing aggro'.
Bonus explanation:
Calldown -- A skill from the Precision Strike tree, i.e. Napalm, Smackdown, or Shock and Awe. From 'calling down an artillery barrage'. I find the term 'Precision Strikes' for this skill tree to be something of a misnomer, especially since you are not using any sort of laser targeting for it.
Aggro -- Common MMORPG term (picked up from Guild Wars) for enemy aggression, that is, which PC the enemy monsters (mobs) are targeting. For instance, a guardian might precede other PCs into a room and perhaps use taunts to ensure that all the enemies are attacking him, since he's more capable of surviving such an onslaught than his allies are. This is called 'grabbing aggro'.
Bonus explanation:
Calldown -- A skill from the Precision Strike tree, i.e. Napalm, Smackdown, or Shock and Awe. From 'calling down an artillery barrage'. I find the term 'Precision Strikes' for this skill tree to be something of a misnomer, especially since you are not using any sort of laser targeting for it.