The Third Position is a political alignment that claims to transcend the Western left-right political scale, as well as the Marxism-Liberalism scale. It is typically associated with fascism and Nazism.
The reason Marxists reject the idea that fascism and Nazism represent a true "third position" is because fascism is based in bourgeois property, it is a pseudo-revolutionary aesthetic promoted by the ancien regime in order to stabilize the decaying liberal order.
Despite similar nomenclature and demonyms (Third Positionist and Fourth Positionist), it is not similar to the Fourth Political Theory, which is a move beyond liberalism, Marxism and fascism.