The Veil

The Veil is a paracausal entity or artifact which is connected to the Traveler. Its existence was revealed to the Guardian by Rasputin in his final message, stating it resides in a hidden Neptunian city and that it is of immense paracausal power. It is used by Neomuna as a power source for the city, and the paracausal energy field it projects forms the basis of Neomuna's CloudArk.

Overview
The Veil somewhat resembles a plant or jellyfish, with a bulbous, cup-shaped main body, branching root-like tendrils that can rapidly grow and generate an indestructible dome, and a large, brightly glowing white hole underneath. Its upper surface has a large circular opening, within which is what appears to be an energy field decorated with intricate blue and purple patterns.

History
The origin and true nature of the Veil remain unclear; it is unknown if it was created by the Traveler or accompanied it when it arrived in the Sol System, and its precise connection to the Traveler has yet to be revealed. Nezarec describes it as the "the sapid secret of the Witness' first victims," suggesting that it may be connected to the Witness' origins.

According to the Lore book Warp and Weft, the Veil is an "artifact of Darkness". It has long been of interest to the Vex of the Sol Divisive, who attempted to create a replica of the Veil in the Black Garden - the equally mysterious entity known as the Black Heart.

The Collapse
During the Collapse, the Disciple of the Witness known as Nezarec led the Black Fleet's assault on Earth, and managed to secure the Veil on his Pyramid (it is currently unknown exactly how he came to be in possession of the Veil). However, he was betrayed by Savathûn, who killed him, cursed his remains and spirited the Veil away to Neptune.

The Veil would later play a central role in the founding of Neomuna, serving as the main power source for the city and the basis of its CloudArk infrastructure. An Ishtar Collective facility was constructed around it, to study it and keep it safe.

Lightfall
After the Witness received a vision of the Veil on Neptune, Calus and his Shadow Legion invaded Neomuna and attempted to use the Radial Mast to establish a link between the Veil and the Traveler. They were ultimately unsuccessful as the Mast was destroyed, but following Calus' defeat the Witness was able to link with the Veil by taking control of the Guardian's Ghost. This caused the Veil to emit an energy beam that allowed the Witness to open a portal on the surface of the Traveler.

Asher Mir discovered information on the Veil independent of the Guardians and the Witness while traveling through the Vex Network, and devoted an unknown amount of time after the Arrival of the Black Fleet to researching and manually simulating it. He was able to achieve a full simulation of the Veil and send the data to Earth, though doing so cost his life as he was forced to resume his integration into the Vex Network to gain access to the necessary resources.

Trivia

 * A number of pre-Lightfall Lore entries make reference to a mysterious "veil", which may or may not refer to the Veil itself:
 * The Lore entry 'Reextinction' contains a dialogue between the Nine in which they make reference to "laying themselves bare before the veil".
 * The Lore entry "Irrealis" contains the phrase "somewhere, a veil is always lifting" in reference to the timeless nature of the Black Garden.
 * The Lore entry "The Witch" describes a "falling veil" that will soon snuff out the Light of Guardians.
 * Bungie have stated that information about the true nature of the Veil will be revealed in Season of the Deep.

List of appearances

 * Destiny 2
 * The Witch Queen
 * Season of the Seraph
 * Lightfall