The call to you is 5€ into a 20€ pot. Your strict pot odds are 4:1, but you suspect two more players will call. You can add those extra values in to determine your implied pot odds: you need to put 5€ into a 30€ pot, giving you a somewhat better 6:1 implied odds.

To continue the example however, assume that was the turn bet in a game of holdem. You still have one more betting round and you suspect the better will again put 5€ into the pot. You suspect again the additional two callers. That means, without your contributions, the pot will be 45€. You need to put in 10€ to call, giving you implied pot odds of 4.5:1.