Party roles are the standard division of labour in a group of characters, most commonly tank, healer, and DPS. The tank absorbs enemy attention and damage, the healer restores health and removes harm, and DPS characters defeat enemies.
The three role model, often called the trinity, became standard in multiplayer RPGs because it makes group fights readable. The tank stands closest to danger and uses taunts and defensive cooldowns to hold aggro. The healer watches health bars more than enemies, deciding who can wait and who needs help now. DPS characters focus on damage and on fight mechanics such as interrupts and moving out of hazards, since they have the least margin for error when hit.
Each role depends on the others in a strict chain. If the tank fails, enemies reach the healer. If the healer falls, the tank has no recovery. If DPS is too slow, even a stable fight runs long enough for resources or a timer to fail. That interdependence is the point: success is a group property, not the sum of individual performances.
Many games bend or break the model on purpose. Action games give every character self healing and dodges, solo games fold all three jobs into one character, and some RPGs use support, crowd control, or hybrid roles instead. The trinity remains the shared language players use to describe who is doing what in any group, even a group that ignores it.
In play"I will queue as healer, so we still need one tank and two DPS to complete the party roles."