Now in a rotating content mode, The Proving Grounds is the latest new edition to Destiny 2's strike lineup. Strikes are basically small PvE content that can be run for rewards in about 20 minutes or less. They follow a short path toward defeating some end boss or accomplishing some goal.
The Proving Grounds, along with the Devil's Lair and Fallen S.A.B.E.R. rotate in to the Destiny Content Vault with the current Season of the Chosen. While Devil's Lair and Fallen S.A.B.E.R. are actually Destiny 1 strikes that have been updated, Proving Grounds is an entirely new set piece, culminating in an epic boss fight against waves of attackers. Find it in-game now with the Season of the Chosen.