JSIK Share definition Flag Acronym: shorthand for "Just So I Know", used in corporate emails. Similar in use to JSYK (Just So You Know), another way of saying FYI. JSIK, I have 2 wks of vacation this year, right? JSIK by Unkie Al May 28, 2006 0 0 Get merch Get the JSIK mug. Buy Now — $32.95 See more merch
