It's the same as pot odds, but instead of including only pot size and opponents bet you also include his remaining stack.
So for example:
You have FD on turn, pot is 5$ (you and your opponent have 45$ left), and he bets 5$. This gives you the pot odds (I presume you know how to calculate this) of 1:2, which is 33%. And your equity on hitting your Flush is approximately 18% (2x 9 outs), which means there is no way you can call this bet only to be drawing for a flush. But if you are sure he will stack off if you hit your flush, then you also calculate his remaining stack into pot odds, and you get the implied pot odds. So basically, your implied pot odds are then (5$: 55$) 1:11, which is around 8% and with you having 18% equity, this a +EV call.
But whenever you are considering implied pot odds, you have to be sure you will really get that much money if you hit what you are drawing for.
Therefore for example, it might even be +EV, to call (for example) 77 preflop vs a 3bet, if opponent 3bet % is like 1% and you are 100% he only has AA. Because you know you'll 100% stack him off if you hit your set.
But basically as brobz said.