In post-structuralist thought, habitus, a concept defined by Pierre Bourdieu, refers to the total ideational environment of a person. This includes the person's beliefs and dispositions, and prefigures everything that that person may choose to do. The concept of habitus challenges the concept of free will, in that within a certain habitus at any one time, choices are not limitless -- there are limited dispositions, or readinesses for action. A person is not an automaton, for there exists flexibility in a habitus, but neither is there complete free will.
A large part of the concept of habitus is that it brings attention to the fact that there are limitless options for action that a person would never think of, and therefore those options don't really exist as possibilities. In normal social situations, a person relies upon a large store of scripts and a large store of knowledge, which present that person with a certain picture of the world and how she or he thinks to behave within it.
A person's habitus cannot be fully known to the person, as it exists largely within the realm of the unconscious and includes things as visceral as body movements and postures, and it also includes the most basic aspects of thought and knowledge about the world, including about the habitus itself.