https://www.gamespot.com/articles/destiny-2-psa-what-you-need-to-know-about-the-week/1100-6453247/

If Destiny 2 is your first Destiny game, or you simply didn't play much of the original, one thing you may be unaware of is how certain parts of the game run on a schedule. By now, you may have noticed that certain things reset daily, but more significant are the those that happen on a weekly basis--the aptly named weekly reset.