EV is short for expected value, which is the amount a gambler can expect to make in the long term over many trials.
@Tenspro2002 used the example of a 50% profit boost on a single -110 bet. This bet is going to +EV: it doesn't matter if you happen to lose on 1 specific game, the bet will make money in the long term because the odds are in your favor.
You mentioned you are a poker player and EV comes up in poker all the time. The simplest example is if I go all-in pre-flop and you have pocket aces, you will always have a +EV call. Even if I have pocket kings and flop a set, your call is still a longterm winning play.
A regular -110 sports bet can potentially still be +EV if you have a big enough edge over the sportsbook that you can overcome the vig when you pick winners. It's pretty hard to get to that point though, and I can recognize that I'm not there. Even when I see a line that looks attractive to me, I won't bet it because I know I don't have the edge.