We Love the King Day is a game element and special event in Civilization V.
Throughout the game, one or more of your cities will periodically request that you acquire a specific luxury resource. If you do so, the city will go into "We Love the King Day" for 20 turns, during which the city's growth rate is increased by 25%. When the 20 turns are over, the city will demand another luxury resource. Filling that request will cause the city to resume WLtKD for another 20 turns.