Having some time to kill early in the morning at work, I figured I'd move on to implicit odds, if the same readers want to know more about that, as well:
Where pot odds take into consideration the money that's in the pot right now, implicit odds is an estimation on how much money you CAN win from the bet if you hit one of your outs. For instance, with 100 in the pot, and a bet of 20, is your gain really only 100 if you win? Can you really not squeeze out an extra few bucks from your opponent if you hit your flush? You probably can - and so as the pot will get bigger, your implicit odds go up.
A good example of when implicit odds come into play is when you limp in with a small or medium pair before the flop in hold 'em. Your chance of hitting a set (which is typically the only way a small or medium pair will win) is around 7.5-1, which means that pot needs to have 6 or 7 other limpers to make it worthwhile. But, of course, that's presuming that everyone will fold if you hit your set, which is rarely the case. Let's say instead that you get four other limpers and will narrow the field down by 50% on the flop, and another 50% on the turn - what are your implicit odds?
Four limpers to the flop = 4 SB.
Two callers to the turn = 2 SB.
One caller to the river = 1BB = 2 SB.
Here, you stand to win 8 small bets, at the initial price of 1, which gives your call positive expectation. By this count, your implicit odds are good to make this pre-flop call with a weak pair because of the money you'll figure to win if you do hit your set, rather than the amount you're "guaranteed" to win.
Here's the downside to implicit odds though: They're an estimation, and as it so happens, people tend to be way too optimistic in calculating them. For instance,
on a board with
gives you 9 outs to a flush, which is a 4-1 shot. Now let's say that there were only two of you in the pot, one limper and you in the BB. Flop was checked around, and he bet at the turn after you checked, the pot would be about 2BB. You're paying 2-1 to see the last card, which could give you the nut flush - but do you call? Pot odds say no. Implicit odds likely don't give you the numbers you're looking for either, but this is where people get overoptimistic!
If your opponent paired his ace and has no hearts, would he really bet into a four-suited board after the river? Would he call your bet? Probably not. You can hardly figure to win more than the money that's already in the pot at the turn, because if you make your hand on the river, he's not going to pay you enough. Even if he calls an extra bet on the river (maybe he has J♥), you're still not getting good enough odds. At that point, your call on the turn will have cost you 1BB, and you're looking at a profit of 3BB, which gives you 3-1. You'll have to successfully checkraise him (and he has to call your checkraise) for it to be near profitable, and you have to succeed at that every time that you hit your flush. Hardly likely.
I know some players who think this is mathematical mumbo-jumbo and has no place in a gambler's heart, but this is really the principle that separates winning players from losing players: Being able to tell a profitable bet from a non-profitable one. In the example above, there's a non-profitable bet being offered. Don't take it.