EV = Expected Value. How much value you expect to make on a given move, be it bet check raise etc

Variance = Sometimes you can play absolutely perfectly and still lose due to a shitty turn or river card. Sometimes this can happen 5 days in a row. This is variance. Its just the term for those up and down swings we all get

Fold Equity = Lets say I have a flush draw and two overcards. So I haven't made a hand yet. Our opponent bets, and we RAISE. We do this because of fold equity. Our villain will fold a better hand x% of the time, and that x% adds money to our pocket, in addition to the fact that we could turn our flush or hit one of our overcards. Remember the fundamental theorem of poker?

Maybe someone else can think of a better example, that ones not the best.