Well, the original poster (Myke) said he has seen the word used but never really understood what it meant. Giving the actual definition without the practical way it is used in this forum will only confuse him. He will have a formula and know it's an amount, and then he'll see someone say "you have more fold equity at 50NL". No amounts mentionned?! Ofcourse the actual definition never hurts, but in light of his question, I think the more intuitive explanation actually helps him out more.

I'm also a bit confused why you bring in whether it would be +EV or -EV. If they are more likely to fold, your fold equity is higher. Whether your play is +EV or -EV on the whole is irrelevant to the concept of fold equity.

Oh yeah...
Still not to big on reverse implied odds.
I'm not sure about all the situations this concept would apply in, but an example will help I think:

Say the flop is three clubs. Your opp bets, and you are holding the jack of clubs. You might think "ok I'm gonna call his bet b/c of pot odds that I hit my flush". However, this is possibly a situation with reverse implied odds. If your opponent holds the A/K/Q of clubs, you are gonna lose a little if you miss (no 5th club shows up), but you'll be losing your stack if your draw completes. If your draw will complete what is only a second best hand, you have reverse implied odds.