The role trinity effectively breaks down classes into roles that serve to focus their kits to deal with one of the three basic types of interaction between NPCs and Players in a "battlefield".

DPS deal with Player>NPC
- Can be CC, Combos, Priming enemies for further damage, or simply going on the offensive.

Tanks deal with NPC>Player
- Getting the enemy attention, creating cover, intercepting attacks and mitigating incomming damage, simply put defending the party.

Support deal with Player>Player
- Its probably the most vague as there are a lot of ways to "assist" teammates, hell even tanking could be considered specialized support. Healing is a pretty straightforward one, but they can buff allies, shield them, give them mobility or anything that makes them more effective at their role.


In the end, all roles have to deal with those three interactions, as all roles must be at least be able to attack, recieve damage and party up. Support is the most ambiguous one as "helping" the party can come in many forms, but is usually the role that most conforms to the game's internal workings as it is the role that can make or break the game systems.