1: not sure i've ever used the word -- i suppose i kind of treat it (in the discussion of others) as a marker for "nothing is decided yet"
2: the social issue of what can be taken to be known, and what is still being debated, is an exact cultural map of many (most? all? i don't know) pressing political conflicts
3: by relativists, some people seem to mean "those guys who are too complacently or vaingloriously superior, and/or cowardly, to take a stand on what they believe -- who argue that "the other guy may have a point" even when the "other guy" is some kind of crusading n4zi or similar"
4: what they think is at stake is the secureness of the institutions of established reliable knowledge