Final Fantasy define the players available actions by classes and their advanced form, jobs, which is why some guides have the class and job name.

Jobs place the player on a system commonly known as the holy trinity. This system assigns a specific focus to the class.

Tanks are the designated target for enemies, with plenty of skills to keep the enemy attention.

Healers keep, as the name implies, the party hale and healthy.

Damage dealers focus on making the most damage in the least amount of time, to end fights as quickly as possible. Because of they, they are also refered to as DPS (Damage per second).

Of note, the above indicates only what the class is meant to focus on, does not mean, as an example, that the healer wont do damage, or that the damage dealers don't have healing or utility spells.

Final fantasy also splits the classes by another type of focus, martial or magical, reflected in game by referring to the classes as Disciplines of War, or Magic. This leads to another split of the classes in their designated functions as damage dealers. So you'll see them split in this list as ranged or melee, physical or magical. This does not mean some ranged classes do not have close combat capability and in general every class will have some ranged ability they can use.