Master and slave philosophy
The "slave revolt in morals" is when the weaker people force their weaker values onto others. This happens when they get resentful about being beneath the stronger people. When these values spread, they favour the weak and priestly people at the cost of the better and nobler people. Nietzsche also says they are life-denying values, meaning they have a negative and unhealthy attitude towards living. They are what make morality dangerous. Nietzsche does not say slave morality is always bad though. Instead, "the ideas of the herd should rule in the herd—but not reach out beyond it". What this means is that weaker values  be for the weaker people but  for the nobler people. Before Nietzsche, the Russian nihilist Dmitry Pisarev had also said extraordinary people should free themselves from morality and priestly ideas.