Trance is a recurring status effect in the series.
Trance is a status exclusive to Terra through the usage of the Trance command. It doubles the damage of Terra's physical and magical attacks except for attacks that ignores Defense and halves all magic damage Terra takes except from attacks that ignores Defense. The status is removed once Trance ends, Terra uses the Revert command, or the battle ends. It is never named in-game.
Trance doubles the power of a party member's spells.
Trance denotes a variety of processes, ecstasy, techniques, modalities and states of mind, awareness and consciousness. In general, it simply means 'idle and motionlessly resting' or 'mesmerized'.