Can you explain to me the difference between discourse and narrative?

I hang around a lot of academics and I go to a number of academic talks. I recently started going to the anthropology talks, and this word, “discourse,” kept popping up. It seems to have something to do with a way of thinking by a certain portion of society, or a kind of contemporary myth that justifies this way of thinking. It sounds like a social narrative to me.

So, what does discourse mean in this context, and why do they use the word so profligately?