Brawler is a gear perk that increases your melee damage. It makes machete hits and other close attacks finish enemies faster.
Melee strikes hit harder, so you need fewer swings to drop an enemy who gets close.
Wear one of the gear pieces that carry it: Clown Hands, Danny's Watch, Rioter Gloves MK II. Each piece only takes one body slot, so plan around the other perks you want.
Worth it for melee-heavy players. If you rarely swing your machete, another perk will help more.