The system in which you determine how much your bet will return at a sportsbook should your bet prove successful.

There are two major systems of odds.

The first is x to y. That is, for every y dollars you bet, the sportsbook will match you x dollars. Therefore, when something is unlikely, x is greater than y, but when something is very likely, y is greater than x. When something has an equal shot of happening as not happening, x is equal to y, at 1 to 1. These odds are not actually created based on the likelyhood of the event, but rather, the odds which will create the most bets on both sides.

...

The other system is per 100 dollars.

For instance,

Lennox Lewis (-500)
Vs.
Some pasty white kid (1200)
In this circumstance, if you put up 100 dollars on the pasty white kid, and he wins, you'll get 1300 dollars back, for a profit of 1200. If you bet 500 dollars on Lennox Lewis, and he wins, then you get 600 dollars back. The - denotes the price to win 100 dollars back.

These lop-sided bets happen more often at rates like -220, which is still an awful bet. People think, "Well gee, Greg Maddux is -220 against the Marlins, so i'll have to put up -220, but it's a sure bet!", and a few times the underdogs actually win, and the morons who put up cash on -220 lose all of their cash!

Of course, sometimes, the sportsbooks make a bad bet, and lose millions of dollars.

But don't cry for vegas, they have millions more where that came from.