Abilities in Bravely Default are split into two categories, as shown below.
Support abilities enhance a character using slots, in their stats or by granting additional effects. They are unlocked by leveling up jobs to the required level. Some abilities, usually the more powerful ones, require the use of multiple slots to equip. These slots are unlocked as the player progresses through the game and awakens the crystals. Each successful awakening rewards the player 1 extra slot, for the grand total of 5 slots per character.
Command abilities must be equipped to be used, and are usable in battle. Each job grants its own command ability skillset, while several abilities such as Attack and Item are universal across all jobs.