Bet: no, really — some people don’t understand what a bet is. Or they might think that a bet and a wager are two different things. Don’t laugh; I still have trouble remembering the difference between odds and lines. Basically, a bet is when you put money (or something of value) on an event with an uncertain outcome. This goes for any kind of bet — a bet in poker, spinning the reels of online slots, or investing in the market.
You have to understand that there is a risk (unlike, say, opening up a bank account, where you never really expect the bank to fail, or that your savings will ever yield anything other than the stated percentage). There should also be some chance that your money will increase or decrease proportionately to the likelihood of the outcome.
Conveniently, that describes odds. The chances of something happening are the most important factors in any kind of betting. Even odds (“even money“) means that you stand to gain exactly as much as you bet (all else being equal, if you win, you double your money).
Proposition bets (props) are made on whether an event will happen or not. “Will Cleveland win the World Series” is a proposition bet.
Handicapping is a way to deal with more than one outcome. For example “Will Cleveland or Florida win the World Series?” couldn’t offer the same reward for a correct choice, because the smart money would always choose the favorite. The bookie handicaps the odds so that together they make even money bet between the two teams.
Anything with better-than-even odds refers to a favorite, or something which is considered likely to happen; these kinds of bets only ever win you less than you bet. Conversely, anything with worse odds is called an underdog, and can more than double your money if you win. In every game with two teams, the favorite and the dog are handicapped to make an even money bet between them.