An Aetheryte is a massive crystal which can be found throughout Eorzea. These crystals allow for players to travel great distances in an instant. Aetherytes are one of the primary ways of fast-traveling across the game world.
Aetheryte is the name given to massive shards of crystallized aethric mist, precisely cut and fused with arcane machinery. While it is not known when or by whom these devices were originally constructed, their teleportation qualities have become the backbone of everyday transportation throughout the realm, with most operated and managed by individual city-states.
Though the exact mechanism behind teleportation via aetheryte is still largely unknown, one theory states that when a sentient being approaches one of these portals, the aether that makes up its body resonates with the aether of the crystals, which in turn results in a complete breakdown of the being's mass, allowing it to temporarily return to the invisible aetheric streams that course throughout the planet. The being's soul, which cannot be broken down, then guides the particles to a pre-determined destination, and upon arrival, the corresponding aetheryte receptacle reconfigures the mist back into its original form. The whole process takes only a matter of moments, allowing for nearly instant transportation to faraway destinations.
However, being broken down into the aetheric level can take its toll on one's body, and the rest is often required after several consecutive jumps, especially as the distance becomes greater. As a precaution, most city-states strongly discourage over-teleporting, as it can lead to irreversible damage...
According to ancient and medieval science, aether (Greek αἰθήρ aithēr), also spelled æther or ether, is the material that fills the region of the Universe above the terrestrial sphere.
The word αἰθήρ (aithēr) in Homeric Greek means "pure, fresh air" or "clear sky", imagined in Greek mythology to be the pure essence where the gods lived and which they breathed, analogous to the air breathed by mortals (also personified as a deity, Aether, the son of Erebus and Nyx). It corresponds to the concept of आकाश (akasha) in Hindu philosophy and is linked to Brihaspati (or the planet Jupiter) and the center direction of the compass. It is related to αἴθω "to incinerate", also intransitive "to burn, to shine" (related is the name Aithiopes (Ethiopians)), meaning "people with a burnt (black) visage".