ultraleftism

Usually The ideology of the ultraleft, associated with left communism, characterized by a rejection of both social democracy and state socialism in favor of traditional Marxism, including opposition to Leninism and the vanguard party.

Broadly, Specifically, Usually Italian left communism; Bordigism.

Derogatory, Usually Extreme or uncompromising leftist ideology, especially strict adherence to orthodox Marxism.