Louis Althusser

"Historical materialism" relates to Marx's belief that everything in society is determined by the things that we produce in order to live. In this theory of history, which is a theory for why things happened the way they did, Marx argues that society has progressed as a result of its material conditions (the things we have produced and the ways we have produced them) rather than a result of ideas and human thought.

Put simply: The most determining factor in society is the goods that we produce and the methods that we use to produce them.

Marx believed that society is divided into the base and the superstructure. The base is comprised of the material aspects of society and it allows for the production of goods. This includes the means of production (factories and tools, for example) and the relations of production (the roles performed by those involved in the production of goods). The superstructure, on the other hand, consists of all the other aspects of society, including culture, ideology, social institutions, political systems, and the identities that we subscribe to. According to Marx's beliefs, the superstructure is shaped by the base.  In turn, the superstructure legitimizes the base by portraying what might be unjust and exploitative as natural.

You can find out more about this idea here. 

Put simply: Society is built upon the ways in which we produce things, and this base is maintained through superstructures that legitimize those processes.