What do you mean by rationalism?

I’ve been lurking here a bit, and am trying to understand what people here mean by rationalism. Many articles here seem to refer to discussion participants as rationalist while meaning very seemingly-different things, including intelligent, socially awkward, well-educated, and unencumbered by education. I’m trying to make a little more sense of the word/​concept.

Surely it does not refer to rationalist in the empiricism/​rationalism divide, because it doesn’t seem to be used in quite that way.