The definition of Fold Equity is: The percentage chance your opponent will fold to this play calculated in chips that are yours due to the percentage chance.

Lets say there's a 15% chance your opponent may fold a 100 dollar pot to you.

That means making that play gives you $15 dollars just by making it. This at first glance, seems like a bad play. Which is why pure bluffs are so bad, there is rarely enough fold equity in comparison to the amount you have to bet.

If you bet around a pot sized bet, with a 15% chance your opponent is going to fold, you've wasted a ton of money.

The reason the calculation is equitous, is because Let's say you make a flop bluff with say, the nut flush draw. Your opponent bets out a pot sized bet, and you raise 3 times that pot sized bet on the flop. There is a 15% chance your opponent will fold here PLUS the 19% chance you'll hit your flush on the turn PLUS the very good chance (Say 95%) that your opponent will let you see the river for free bringing you up to like a 35% chance to hit your flush.

So that Bluff may end up being worth about 50% of the pot.

Which is ALWAYS good.

Finally the percentages I threw around are almost all opponent dependant. One opponent may fold to that bet 100% of the time, another may never fold to that bet. It's up to you to gauge.

The only percent that is static in this whole post is the chance to hit your flush by the river.