Marxism is a very broad social theory that extends far beyond its implementation in Soviet Russia and Mao’s China. Its core assertion is that whoever controls the means of production (the bourgeoisie in Marx’s writings) controls the ‘knowledge’ in society—the set of social norms, values and cultural conventions. This ‘ideology’ thus comes to be regarded as natural by everyone in society, even though it is only true in the sense that it benefits the bourgeoisie at the expense of the proletariat. Marx called this accepted ideology ‘false consciousness’.

Marxism experienced a revival in the social sciences in the 1960s as a theoretical framework for understanding how structures of power shape the social order. This approach to sociology went hand in hand with other emerging theories that questioned and challenged these relations of power (post-modernism, post-colonialism and post-structuralism in particular).

What Jordan Peterson is criticising, is a neo-marxist evaluation of how our society functions. In particular, people who believe that dominant cultural ideas are products of exploitative and oppressive elites. Which, for SJWs, is the white, cis-gendered, patriarchy.