What are secondary targets and which skill involves?

Question

In Torchlight 2 it happens to found weapons with attributes like +75% damage to all secondary targets. But what does it mean? Who are secondary targets and which skill affect them?

Answer 1

I believe that "secondary" targets are essentially those who are damaged via a weapon's splash damage. From one of the load-screen tips:

Most melee weapons do Splash Damage, hitting adjacent monsters in an arc in front of you. Two-handed weapons have longer and wider arcs and do a larger amount of damage to these Splash targets.

So, the weapon you picked up will modify the amount of damage done to targets hit by splash damage (i.e. not the individual monster you are actively attacking).