so far (Adverb) — Used in negative statement to describe a situation that has existed up to this point or up to the present time. ex. "So far he hasn't called"
so far (Adverb) — To the degree or extent that. ex. "so far as it is reasonably practical he should practice restraint"
so far (Adverb) — Used after a superlative. ex. "this is the best so far"