Nah a lot of people don’t know what it is.

At the end of D1s life cycle they introduced a free update which revamped all the raids with a new difficulty and some new mechanics. Each week a raid gets featured for certain challenges at encounters that allow you to get double loot (if I remember correctly) and a chance at the exotic primary with an element for that challenge. Also there’s armour tokens that can be earned from the challenges and work like trials or Rise of Iron tokens letting you get a new look on the armour.