Levels are stages you reach as you progress through the game. Most actions you undertake award XP (Experience) and this is what progresses you towards your next level. As you reach new levels, you are rewarded with some Coins and Water, and new items and goals are unlocked. Your watered crops and trees are instantly ripened and all adult and prized animals will become hungry again.
In late 2014, Zynga lowered all the XP xp required to gain levels. As of winter 2016, there are a total of 320 levels.