Destiny 2's Daily Challenge is an objective you can complete as part of Iron Banner.
Completing a Daily Challenge is useful to increase your Iron Banner rank boost, and is also a requirement for completing the Forging Iron quest.
Of course, you need to find what the Daily Challenge in Destiny 2 is first - which this page can help with.
How to complete a Daily Challenge in Destiny 2
The Daily Challenge is an objective introduced in Iron Banner as part of the 'rank boost' system - but you'll likely first come across it as you complete the Forging Iron quest.
To find the Daily Challenge in Destiny 2, go to the Director screen, select Crucible, then hover over the Iron Banner node. On the bottom half of this explainer will be the 'Challenges' - this is the Daily Challenge you must complete.
For example, in the first week of Iron Banner in Season 18, the first Daily Challenge is 'Complete Iron Banner matches as either Arc or Stasis subclasses'.
Confusingly, it says 'Weekly'. This is because there are four Daily Challenges across the week, with one new Daily Challenge rolling out per day - on the Tuesday, Wednesday, Thursday and Friday daily reset.
You can either complete them as they unlock, or save them up until Friday onwards - whichever you prefer.
Besides completing the Forging Iron quest step, the benefit of completing Daily Challenges is it can increase your rank boost during the event.
If you select Iron Banner, then hover over the Rank Boost node in the bottom right, you can see your current boost based on various elements - including how many Daily Challenges you have completed.
If you are serious about ranking up during Iron Banner - which is all the more important now it only appears two weeks per season - then having as many rank boosts active as possible will be a priority, especially if you also want to unlock an Allied Demand along the way.
Enjoy this year's Iron Banner!