From Destinypedia, the Destiny wiki
Deepsight is an ability granted by the Darkness. It is a form of clairvoyance, allowing one to see through illusions and see echoes of past events.
Deepsight is used to reveal platforms, solve puzzles, open certain chests within Savathûn's Throne World, and enable weapon crafting at the Relic on Mars by first obtaining a weapon pattern, then shaping it by spending Resonant Alloys, Glimmer, Enhancement Cores, Harmonic Alloys found exclusively in Raids, as well as Legendary Shards, Enhancement Prisms, and Ascendant Alloys once the enhanced traits are unlockable by leveling up the crafted weapon, then reshaping it. Deepsight is also used by the Lucent Hive to hide chests guarded by the Lucent Executioners through a material called Qualichor.