Implied pot odds, or simply implied odds, is the pot odds calculated by factoring in additional bets you can win later on if you do hit your hand.
You are on an open-ended straight draw. You have a 1 in 5 chance of making your straight on the next card. There is $50 in the pot. Your opponent bets $50 and has $200 left in his stack. You know your opponent to be a very loose and aggressive player and is likely to possess a top pair and will almost certainly move all-in later on.
Current pot odds = amount in pot/amount to call = $100/$50 = 2:1. Playing by the current pot odds, it will be unwise to call his bet.
However, the implied pot odds = (amount in pot + expected future bets)/amount to call = ($100 + $200)/$50 = 6:1.
Hence the implied pot odds suggests that it makes sense to call his bet.