In Guild Wars 2, just about every profession can be any class, as long as it’s setup with the right skills and weapons. Damage in particular is when a profession has a skill set that focuses primarily on damaging targets with as much DPS as possible. [A list of all GW2 classes]
This is the most basic class in Guild Wars 2, most default spvp profession builds are damage, and most if not all professions can be damage. [Guild Wars 2 main page]
Damage usually focuses on heavy hitting attacks, stuns, damage over times, summons, and more. This class is not very good at healing, buffing, or debuffing.
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