By the spirit of revenge, Nietzsche means a very great variety of phenomena. And to some of them he alludes in this speech. In his other writings, he [uses] a French word, ressentiment— which in Nietzsche does not merely mean resentment, but rather the reaction of those who are disadvantaged by nature and/or law against the privileged. And that leads in a deeper stratum to a denial of the superiority of the goodness of the advantages in question, [to a] denigration of those qualities and the longing for the humiliation of these people in this life and in the next.

Seminar on Nietzsche's Beyond Good and Evil (1971-1972) - Session 1