Zombies, the most common of the reanimated corpses to appear in mass media, are inspired by Haitian Folklore. A bokor, a Voodou witch, would raise the dead to serve their own purposes. These zombies have no will of their own, as the bokor controls their souls.
Zombies that appear in most modern fiction deviate a bit from this origin. The Zombie Apocalypse has become a popular archetype, where a widespread outbreak of zombie attacks plauge the globe. When humans get attacked by zombies, a zombie virus will spread and infect them, turning them into the undead. This type of zombie is popular in the series The Walking Dead, as well as being parodied on an episode of Community.
As in the movies and television, zombies generally attack in large groups, whether with their kind, or other undead. In the first Final Fantasy, it's not too uncommon to fight six to nine undead in one battle. Fortunately, the undead in this series are weak to not only Fire and Holy magic, but also Curative spells.
Zombie is also the name of an ability and status affect. The ability/spell will inflict said status affect, which turns the target into the undead. This makes Curative magics lethal and Death Spells beneficial. In games like Final Fantsy V, the player loses control of the Zombified character. The Necromancer job or anyone equipping the Bone Mail has a similar status, without losing control of the character.
Another popular undead archetype is the Ghoul. Ghouls are known for feasting on human flesh. They are derived from Arabian Folklore, where they were shapeshifting desert demons, as opposed to the modern interpretation of graveyard dwelling monsters. One of the oldest accounts of ghouls is in A Thousand and One Nights.
It was most likely George A. Romero, who combined the reanimated corpse of the zombie with the cannibalistic qualities of the ghoul in his The Night of the Living Dead, which gave ghouls their undead status.
Ghouls regularly appeared in the Dungeons & Dragons series of games. Ghouls are
Revenants are similar to both zombies and ghouls. From Medieval Folklore, they are the reanimated corpses of those who lived "wicked" lives. Their myth is similar to those of Vampires from Balkan Folklore. However, the connection between the two has been questioned by scholars, as Vampires hadn't been introduced to Western Europe until far after the Middle Ages. Even so, the similarities are striking. Revenants are known for spreading disease and sucking blood. Like the others, they also appear in Final Fantasy, attacking in mobs.
All of these are really just the tip of the undead iceberg. The undead in various forms has haunted the psyche of society from the earliest of times and continue today as they inhibit our paths to save the world in Final Fantasy. Whether you're going trick or treating, or mowing down Zombies with a Fira spell, don't forget where these frightening legends came from.