In the context of discourse analysis, a 'repertoire' is a way of describing something. It can be a set of words and expressions, perhaps with associated images and so on. If it is a very familiar way of talking about something, we tend not to notice it. For example, many cultures have an apparently familiar way of talking about the perceived world—it is external to the perceiver, 'out there' and factual. Sometimes, though, you will see a person (or a newspaper or other 'author') use different descriptions to talk about that object. That variabity makes us realise that perhaps the repertoire deserves some attention; just because it is familiar doesn't mean it is neutral. So a useful method of discourse analysis is to look for variability: how people's descriptions change.