Damage Per Second is what the acronym DSP stands for, though the meaning of DSPer strays from that a hint. In a gaming context a DPSer is someone who can deal a lot of damage. This is a different stereotype than a tank who is someone who can hit hard and be hit hard. Instead a DPSer can hit harder than the tank but can't really take a beating. It's more lopsided. Think of the frail old man wizard who is throwing a fireball. Healer is another stereotype alongside DPSer and tank in this vein of things. When I actually used to play Dungeons and Dragons there was, from the beginning, the concept of classes such a fighter (tank), a cleric (healer), and a magic-user (DPSer), but the broader containers in which I suppose both fighter and barbarian fall under the broad use of the "tank" term are newer things I've only brushed up against since 2009. These are some geek speak generalities.