https://www.gamespot.com/articles/destiny-2-exotic-weapon-guide-how-to-obtain-mida-m/1100-6453225/

Like in the original game, Exotics are the most desirable items for you to obtain in Destiny 2. While you're sure to get your hands on some through loot drops from enemies or chests, there are also those that you can obtain through a specific process.