Skill Target Forwarding

Skill Target Forwarding is an option (accessible under Options | Combat Options) which causes skills to be "forwarded" through a character's target (affecting the target's target) rather than applying directly to the target. For example, a DPS character in a group could target the group's tank, and with Skill Target Forwarding enabled their attacks would affect the tank's target. Healers can similarly target a mob and their heals would then apply to the mob's target (presumably a friendly character).