The 'Base and Superstructure' is a foundational concept in Marxist theory, where the 'base' refers to the economic foundation of society, including the means and relations of production, while the 'superstructure' encompasses the cultural, political, and ideological systems that arise from and serve to reinforce the base. This relationship suggests that changes in the economic base lead to transformations in the superstructure, highlighting the influence of material conditions on societal development.