Infusion

Infusion is a feature introduced with The Taken King and boosts the Attack or Defense rating of a favored Weapon or Armor piece, similarly to the use of Etheric Light. Infusing a stronger Light-leveled piece of gear into another less powerful one will have the level increased to that of Infused piece, but will not receive any of the perks, allowing for players to choose armor or weapons for aesthetic reasons and still have good "rolls", or perks they like or want.

Destiny
Only Weapons and armor from Year 2 and Year 3 are able to be Infused, due to the feature being introduced in Year 2.

Destiny 2
In Destiny 2, every Legendary and Exotic gear can be Infused with a bit of Glimmer and Legendary Shards. 4 Shards are needed if a Rare item is being Infused into a Legendary or Exotic, while only 1 Shard is required if a Legendary is used for the Infusion.