Social science jargon. “Discourse [is] a system of thought, knowledge, or communication that constructs our world experience […]. [It] is social boundary that defines what statements can be said about a topic.” (from Wikipedia 
)
As with our jargon like, say, “stack frame,” "discourse" is kinda-sorta metaphorically linked to the more common meaning, but it’s the differences that are more important.
Discourse turns what William James called “the blooming buzzing confusion” of reality into something structured, meaningful, and predictable – something that you use to organize your actions and so achieve things in the world.
Discourse comes from a mass of relevant people, and I think of it as the context that determines whether an idea of yours will be seen as sensible or silly. You can predict something from outside the dominant discourse will be seen by its average participant as “not right – not even wrong”, to use Niels Bohr’s phrase.
People differ on how power much the discourse has to affect individual actions and thought.
* You can think of the discourse as a sort of distributed power that pushes people around by shaping their worldview.
* Or you can think of it as gentler, as making some thoughts harder to think but also suggesting others.
* Or you can think you can transcend the power of discourse by some act of will or revelation/epiphany. "I am the master of my fate / I am the captain of my soul. " After that, you'll be free. Good luck!