In Final Fantasy XIV, what is the name of the first expansion?

The first expansion for Final Fantasy XIV is Heavensward.

Heavensward launched in 2015 as the first expansion to Final Fantasy XIV: A Realm Reborn. It continues the main scenario after the events of A Realm Reborn and takes the player to Ishgard, a city-state previously closed to outsiders. The expansion's central conflict is the Dragonsong War, a thousand-year struggle between Ishgard and the dragons of Dravania.

The expansion substantially broadened the game. It raised the level cap from 50 to 60, added the Dark Knight, Astrologian, and Machinist jobs, introduced the playable Au Ra race, and enabled flying mounts in its new zones. Its release date was June 23, 2015, nearly two years after A Realm Reborn.

A common mix-up is treating A Realm Reborn as an expansion, but it is the rebuilt version and relaunch of the original Final Fantasy XIV. Heavensward is the first expansion proper; Stormblood is second, Shadowbringers is third, and Endwalker is fourth. Dawntrail followed Endwalker as the fifth major expansion.