What is the World Level?

As you increase your adventure rank, your World Level will increase as well. This is the game's way of scaling the enemies' strengths to your level and increase the quality of drops at the same time. Later on, you'll even need to complete Adventure Rank Ascension Quests to increase the world level. You don't have to worry about this too much; just continue playing the game and the World Level will scale along with your progress.