Endless is the second mode, where you fight against an endless onslaught of enemies to get points and rise up the leaderboards. (psnstores.com)
These missions have various objectives, such as defend certain points from onslaughts of enemies or kill every enemy in the map. (playstationlifestyle.net)
Rampage pits you against onslaughts of enemies who you must kill to build up your Kleos score and Bloodlust where you are slowly losing health and must continue to defeat enemies to stay alive. (playstationlifestyle.net)