Expected Value (or EV for short) is the focus of every poker player. The goal of winning poker is to make as many +EV decisions as possible, and the higher the EV is, the better the play. In short, a play that is +EV is expected to net us money over the long term while plays that are -EV are going to cost us money in the long run.
The basic formula is simple:
In other words, your expected value of a particular play is equal to the chances of winning multiplied by how much you'll win, minus the chances of losing multiplied by how much you'd lose.