This article is from the Final-Fantasy and other Square Soft Games FAQ, by firstname.lastname@example.org (Nick Zitzmann) with numerous contributions by others.
Samurai [L3 Knight, L4 Monk, L2 Lancer]
Samurai can unleash the hidden powers of Japanese katana blades, which
typically can heal the party or hurt enemies. Moreover, healing katanas
won't affect enemies, and hurting ones won't affect allies. The only
problem is these katanas can be destroyed after repeated use.
Ninja [L3 Archer, L4 Thief, L2 Geomancer]
Ninjas are the fastest characters, can be equipped with two weapons, and
can throw objects & projectiles at enemies. Need we say more? As
warriors, these guys are excellent for sneak attacks. However, their low
armor prohibits them from being too confrontational.
Calculator [L4 Priest, L4 Wizard, L3 Time Mage, L3 Oracle]
Calculators select magic targets based on different calculations - for
instance; the height, level, or experience of the targets. They can
theoretically hit every target on the screen, and their magic is cast
instantly with no charge delays. However, they are the game's slowest
Bard [male, L4 Summoner, L4 Mediator]
Bards can sing songs that affect every allied character on the screen.
Their ability to hit every allied character is their strongest point.
However, since the effects are often rather weak, and the charge time is
rather long, they're not always that useful.
Dancer [female, L4 Geomancer, L4 Lancer]
Same as bards, except their dances hit every enemy on the screen. Just
like the bards, unfortunately, the dances are rather weak.
Mime [L8 Squire, L8 Chemist, L4 Summoner, L4 Mediator, L4 Geomancer, L4
Mimes don't have any commands of their own; instead, they mimic the
actions of the other characters. This has the potential to be the
strongest job in the game, however, the prerequisites turn most gamers
away from this prestigious job.