[KJL]

Say that there is $500 in the pot, you are heads up with an oppenent on the flop. You have JT and you oppenent has A8
The flop comes AK4. Your oppenent bets $100, giving you 6-1 from the pot versus your 11-1 shot hit a Queen on the turn, so based on pot odds you should fold. Now let's say your oppenent will go all in for $600 more on the turn. Now the implied odds give you 12-1 on your 11-1 shot, so you should call the bet on the flop.

That's implied odds. Of course in a real game you do not know what your opponent will do, so you have to use your judgement.