The EV gap from the best hold, added up hand by hand.
Each hand counts "best EV − your EV" per 5 coins, and a correct hand counts 0. Example: the best hold is JJ (about 7.7 for 5 coins), but you keep an ace with it (about 7.1), so you missed about 0.6 coins. The "Missed EV" stat is this total; the smaller it is, the closer you are to the best play.