+EV refers to a positive Expected Value in betting. It signifies that a bet is expected to yield a profit over the long term. A +EV bet has a higher potential return than the risk involved, making it a favorable opportunity for bettors to consider.
The concept was initially stated: A persistent gambler who raises their bet to a fixed fraction of the gambler's bankroll after a win, but does not reduce it after a loss, will eventually and inevitably go broke, even if each bet has a positive expected value.