Lore is the word used to refer to the in game history and collected information of the Warcraft franchise.
Lore can be found in books and previous Warcraft videogames. World of Warcraft tries to flesh out and continue the lore that was presented in previous games.
There have been situations where Blizzard altered or ignored the lore to further gameplay. The expression 'lollore' was coined on the official forum to describe this.