Definition of pot odds
Pot odds indicate the ratio of the bet you have to put in to how often you will hit your draw or how often you will improve your hand. Pot odds indicate whether or not a call is profitable in the long run. Pot odds are often expressed as 2:1 or 3:2 or 4:1. For the 2:1 example, we would say "two to one". Two to one means that out of 3 occurrences, 2 times we will not hit our draw or card and 1 time we will hit.
An example of pot rating in practice
Pot odds are most useful on the flop and turn. They help us to assess the profitability of a call. Let's take an example from a tournament. There are 20 big blinds in a pot on the flop. Your opponent shoves all in his last 10 blinds. He bets 10 into 20. You look at your cards and you have a flush draw. You know that a 2-card flush draw coming up (turn + river) will have odds of 2:1 (twice you don't hit, once you do). Here, you have to invest 10 to win 30. Out of 3 times, you will lose 2 times (so €20 loss) and hit once (€30 win). Wins - losses (30 - 20) = €10 profit in the long run. The pot odds are favourable, you can call!