Many people don’t know the exact difference between equity and EV. In fact, some people use the terms as if they were identical.
Equity is the percentage chance that a hand will win after all the cards are dealt. The percentage chance includes splits and is utilized when comparing your holding against opponent’s hand(s) or range(s).

The term is used in different ways, with or without more cards to come. Without cards to come and your opponent’s hand unknown, your equity is calculated against his likely range. But with cards to come, when all the cards are known, your equity is calculated by your chances after the river card is dealt. In other words, your percentage chances on a runout. But with cards to come and your opponents hand unknown, your equity is the percentage chance against his feasible range.

For example: AcKc has 45.76% equity against TcTh, which has 54.24% equity. That said, equity doesn’t include measuring the implied odds or economic value of the hand. A6o has more pre-flop equity than KsQs, as A6o has around 54% pre-flop equity. But KsQs ought to win more money over time if the stacks are deep because it has much better implied odds than A6o.

The reason being, among other things, is that KsQs plays better against your opponents’ big bet calling/raising range, whereas A6o is likely to get you in many trouble post-flop situations. And the true value of a hand is its propensity to win money, not have the highest equity (unless all-in). That’s because the EV or expectation of some hands is stronger than certain hands with higher equity due to the implied odds being better.

EV is your expectation. It’s different from equity in that EV is the average of what you can expect to win going forward with a given play. Folding at the decision point has an EV of zero even if you have already invested money in the pot. However, if you continue forward with your hand, the value of the chips in the pot at the decision point is calculated into the expected return on your play choice equation.

For example, if you’re heads-up, have a gut shot after the turn as your only win with \$100 in the pot and are facing an all-in \$30 bet, your EV is zero if you fold and -\$18.19 if you call the \$30. You’re 9.09% to make the straight and with \$130 in the pot including your call, the \$30 call returns an average of \$11.81. Since your call cost you \$30, the call loses \$18.19 of EV.

That’s a simple example to explain the concept. Don’t forget to include the implied odds. In reality things get much more complicated as you can’t average together all the possible future scenarios in any given hand. That said, understanding the concept and estimating the EV going forward will formulate crisper decisions. And the closer you get to reality, the tougher you’re going to make it on your opponents.

Additionally, all gambling equations should be quantified in terms of EV/expectation. We’re taught to quantify things nominally. But, when gambling, if you bet \$10 with \$15 expected return on your investment (EV), you’ve made \$5 whether you win the hand or not.
Yeah, I know it doesn’t feel that way, but just keep making those positive EV bets and those chips WILL end up in your stack!