From Destinypedia, the Destiny wiki
Lore are collectibles, originally a category of Triumphs, that were added to Destiny 2 with the release of Forsaken. It is divided into four sections: The Vanguard (added in Lightfall), The Light, Dusk and Dawn, and The Darkness, each of which contains several lore books with multiple entries. With some exceptions, each category is focused on certain subjects. Lore entries are unlocked via finding collectibles throughout the game or completing certain tasks.
Also contained within this page are the Books of Sorrow and The Maraid which were released in Destiny as Grimoire entries, as well as physical books included with expansion Collector's Editions. Other materials include Weblore and the Destiny Grimoire Anthology books, which can be found on their respective pages.
Collector's Edition Lore
The Vanguard category serves to give a basic explanation of the game and its world. All books are unlocked by progressing through Guardian Ranks.
The Light category primarily centers around Guardians, their allies, and the Light.
Dusk and Dawn
The Dusk and Dawn category primarily centers around those caught in between the main conflicts of the series, from entire societies to ordinary people.
The Darkness category primarily centers around the Darkness, and those who would align themselves with the Witness.