Support skills are skills that are part of the Support category in the skill window. These skills generally affect a battle in less direct ways but are still important.
The current maximum value for support skills is 200, so you can max 2 on a character.
They can be divided into the following effects:
Aggro Management
Provocation: Increases the aggro generated by your attacks making yourself more susceptible to being attacked while in group.
Silent Discipline: Decreases the aggro generated by your attacks making yourself less susceptible to being attacked while in group.
Regenerative
Restoration: Increases your action point regeneration in combat.
Survival: Heals self some damage automatically after each battle.
Loot
Scavenger: Increases your chance for finding items.