Prestige

You can get 1,000,000 prestige experience every day (resets at daily reset time) after you hit level 50. Any experience past that will be dropped down to a very low number. Every prestige rank up will give you a reward that you can check in the Prestige Rank panel. Most notably you can get a lot of AP from prestige ranks.
ChojaHiragawa's Guide (Go to Prestige tab): Link
Maple Weeb's Prestige Video: