The Forgotten Realms setting is the "default" D&D setting. Most published adventures take place in it, specifically a small part of it (planet: Toril, continent: Faerun, region: Sword Coast, the west coast of Faerun; this region has a number of famous cities like Waterdeep, Baldur's Gate, Candlekeep, Neverwinter, etc...). The vast majority of lore that you can find in books like the Monster Manual specifically relate to this setting (Volo, Mordenkainen, Tasha, Xanathar, etc... all live there anyway). It also has many famous characters and deities (e.g. Corellon, Gruumsh, Moradin...), countries, cultures, even some languages. And it also includes things like the Kenku curse.

But of course if you're running a homebrew setting like I do, you can feel free to cherry-pick it or just straight-up ignore it.