A society’s superstructure, in social terms, is the ensemble of all non-economic social relations that must necessarily be considered in order to understand the reproduction over time of that society. It’s the political, legal, ideological, cultural, etc. social relations.
Similar to what’s assigned to the relationship between the relations of production and the productive forces of production, a certain superstructure can only exist on the basis of certain relations of production. For example, labour rights of wage relationships can only exist on the basis of the existence of wages. But, at the same time, this superstructure also influences the economic base (the productive forces of production and the relations of production). For example, the Spanish labour counter-reform of 2012, which blew up collective bargaining, influences the relations of production and the productive forces of production, contributing to the increased degree of exploitation, worsening the living conditions of the working class, which is the vast majority of the population.
Social relations situated in the superstructure, like the State or ideology, are crucial for social reproduction, so that questioning them head-on is essential to any emancipatory perspective (on the subject, see the 1917 text The State and Revolution, written by Lenin, who also eloquently said in the 1916 text Imperialism, The Highest Stage of Capitalism,: “the imperialist ideology also penetrates the working class, which is not separated from the other classes by a Chinese Wall”).