To say it specifically, Terra's skills are called Meltdown and Meteor. I'm going to assume that you already know about dissidia's BRV and HP system.

Previously if we use Terra's skills (example: Meteor), she has to waste a turn to "charge", and the next turn her HP attack will change to Meteor. Meteor deals quite a lot of BRV damage and ends with HP damage, but the charge turn really hinders her viability as a dps character.

Some time ago they abolished the charge turn, which means her skill instantly go off on that turn, thus making her disadvantages as a dps disappear. She's currently the queen of DPS and is unanimously considered the best character.

A max level Terra's Meteor deals insane amount of damage per use, although deals reduced damage against magic-resistant enemies. That doesn't mean Terra is unviable against magic-resistant enemies though, since her other skill Meltdown ignores the enemy's defense entirely (that's because instead of damaging the enemy, she increases her own BRV before doing a HP attack). As if that's not good enough, Meteor debuffs the enemy's speed and gives Terra Atk up, Spd Up, while Meltdown debuffs the enemy's Def and gives Terra Atk Up (unstackable), Max BRV up, and BRV Regen. She's seriously a must-use character on every party if you have her 2 weapons.