EV means Expected Value
, and is a measure of your likely winnings (or loss) given average luck.
For example, you are all in preflop holding (say)
, your opponent turns over
and there is $200 in the pot. In this scenario, you will win 82% of the time and lose $18% (there is a small chance of a draw, but it is less than one percent, so we will ignore it for the sake of simplicity). Your Expected Value in this situation will be 200 x 0.82 = $164. In other words, this is the average amount which you would expect to win.
Although you sometimes see the EV calculated out that way during detailed Hand Analysis, it is more usually expressed in general terms. For example, if a particular line of play is described as having Positive Expected Value (usually written "+EV"), that means it is a sound play which will yield a profit on average (though of course it may not do so in a single specific example, depending on the fall of cards).