Lore Book

Lore Books are in-game items that the player can pick up, which will deliver lore and story information via audio files in-game.

Vasadan clarified the mechanics of lore books while grouped during the Diablo III beta[1]:

If you have lore already, it's going to disappear if you click on it. That way you do not get experience points for picking it up, but other people in your party still get the lore if they do not have it.