Korean website Ruliweb has leaked some gameplay information about Final Fantasy III's upcoming port to the Nintendo DS. Namely, a "Defense Meter" of some sort will be present in battles and play as large a role (if not larger) than a character's HP meter.
Characters attacking foes will result in depleting of the Defense Meter while the enemy is shown trying to block the strike. Once the Defense Meter is history, HP can be taken. Reports have not been clear enough to indicate whether the Defense Meters are exclusive to foes or if the playable characters will have them as well.
While a DS port of Final Fantasy III has talked about for quite some time, there are still no release dates known. More information will be reported as it is made available.