A state of mind that, in addition to being stilled and settled (shamatha), is accompanied by an additional sense of fitness -- the subsidiary awareness of feeling totally fit to discern and understand fully the subtle details of anything. Vipashyana is not necessarily focused on voidness or on the four noble truths, although most commonly in sutra it is. Other translators render the term as "special insight."
J. Hopkins: Special insight
Synonyms: Exceptional perception; Special insight