I couldn't miss the chance to practice my drawing!
Triple Attack is an enemy ability used by Fafnir. Triple Attack itself is almost identical to Fafnir's normal attack, the only differences are that it has quick hit properties, and it cannot break the damage limit. However, in the same turn, it is immediately followed with an elemental breath attack, and then another physical attack, thus the name Triple Attack is most likely referring to the three-attack combo as a whole.
Triple Attack is a Thief-only job trait. There are two tiers, available at level 55 and 96 respectively. The exact formula that determines when this is activated is still a mystery. Every once in a while, instead of attacking once, the player with this ability will attack three times. The Triple Dagger and Assassin's Poulaines enhances this ability.
Triple Attack is also an enemy ability that delivers a threefold attack on a single target. It can be used by the Roc family.
Triple Attack is an active physical ability that inflicts neutral physical damage and hits 3 times on a single target for 6 AP. It has high topple strength. It can be used by Ghidra and Trihyde.
Tri- is a numerical prefix meaning three.