Once upon a time, all there was in sportsbetting is what is now called the “moneyline” (or “money line”).

The moneyline is simply the odds that a given team will win a certain game, which is to say, the proportion between the amount of money someone betting on that team has to risk, to the amount of money they stand to win.

When the odds are such that one must risk more than one stands to win, this is expressed with a negative number. For example, if the moneyline on a team is -150, this means you would need to risk $150 to win $100 (or $1.50 to win $1.00, or $15 million to win $10 million, etc.). If the moneyline is -600, this means you would need to risk $600 to win $100, i.e., this team is a heavy favorite.

When the odds are such that one stands to win more than one must risk, this is expressed with a positive number. For example, if the moneyline on a team is +125, this means you would need to risk $100 to win $125. If the moneyline is +1400, this means you would need to risk $100 to win $1,400, i.e., this team is a very heavy underdog.

The problem bookies ran into with moneylines is that most people prefer to bet when there is something closer to a 50-50 shot, so lopsided moneylines tended to get less action. If the moneyline for a favorite on a game was -800, and the moneyline on the underdog was +700 (the reason it’s not the same negative and positive number is because the bookie takes out his cut-the “vigorish,” “vig,” or “juice”), not too many people wanted to risk such a disproportionate amount on the favorite even though they’d probably win, and not too many people wanted to bet on an underdog that was so unlikely to win.

But then in the 1940s (there’s some dispute over who invented it and precisely when) came the “pointspread” (or “point spread” or just “spread”). Now instead of just being able to bet on who would win a game, one could also bet based on the margin of victory.

For example, if one basketball team is moderately better than another, they might be favored by, say, 6 points. The favorite would have a line of -6, and the underdog would have a line of +6. To bet on the favorite at -6 means you win your bet if that team wins the game by more than 6 points. You lose if they either lose the game or win by less than 6 points. You tie (or “push”) if they win the game by exactly 6 points.

Conversely, if you bet the underdog at +6, this means you win your bet if they either win the game or lose by less than 6 points. You lose if they lose the game by more than 6 points. You tie if they lose the game by exactly 6 points.

Betting with the spread like this did not replace moneylines. You can still normally bet either way on most sports. It just added another option that bettors found appealing.

You will often see pointspreads in halves, such as -1.5 or +10.5. This tends to confuse people new to sportsbetting. Teams can’t score in increments of a half point after all, so what’s the point of having spreads that are not whole numbers?

Consider a basketball game with a spread of 6.5 instead of 6 as above, and think about the implications. Now the favorite has to win by more than 6.5 instead of more than 6, and the underdog has to lose by less than 6.5 (or win) instead of less than 6. The difference, then comes if the favorite wins by exactly 6. When the line is 6, that means bettors on both sides tie. When the line is 6.5, everyone who bet on the favorite loses, and everyone who bet on the underdog wins.

In order for the sportsbooks to collect their juice on these pointspread bets, the convention is for bettors on both sides to have to put up $11 to win $10, i.e., odds of -110. This is not universal however. Some sportsbooks to be competitive might use -107 on each side, or -105, or something else entirely.

Furthermore, there are times a sportsbook chooses to not use the same odds on both sides of the pointspread. In football, for instance, so many games are won by exactly 3 points, that there’s a huge difference between pointspreads of 2.5 and 3, or 3 and 3.5. There are times that if a sportsbook offered the game at 2.5 and had both sides pay -110, they’d be giving too good a deal on the favorite and almost everyone would bet that side, whereas if they offered the game at 3 and had both sides pay -110, they’d be giving too good a deal on the underdog and almost everyone would bet that side.

So what a sportsbook might do in that situation is pick one of those numbers but then unbalance the odds. So they might set the line at 3, but to avoid making it too attractive to the underdog bettors, they’ll make it +3, -125, while making the other side -3, +105. So you can either get a better number but pay a little more for it, or you can accept a worse number but pay less for it. In theory, this gives the sportsbook a better chance of getting approximately equal action on both sides.

In sports like football and basketball, the pointspread varies widely depending on the disparity between the teams. In one game a team might be favored by only 1 point (so virtually the same as a moneyline), and in another game a team might be favored by 16.

But in certain other sports, the same spread is offered for pretty much every game. In baseball and hockey, for instance, the spread is set at 1.5. (That’s called the “run line” in baseball, and the “puck line” in hockey.) So if you want to bet the favorite, you can either bet them on the moneyline, or bet them at -1.5. If you want to bet the underdog, you can either bet them on the moneyline, or bet them at +1.5.

The term “side” in this context generally refers to pointspread bets like this on the margin of victory, though sometimes it is used more broadly to refer to any bet on a team, whether on the pointspread or on the moneyline.

The next very common way of betting a game to be invented was wagering on the “total.” This simply refers to betting on how many points (runs, goals, whatever) will be scored in a game by both teams combined.

Really totals are very similar in form to sides. Again the convention is for the bets both ways to be at -110 odds, but again this can vary. Just like with a side bet a line is set and you can bet on either the favorite or the underdog, with totals a line is set and you can either bet “Over” it or “Under” it.

For example, if the total for a football game is 38, this means those who bet Over win if at least 39 points are scored in the game (31-10, 47-37, 39-0, 23-21, etc.), those who bet Under win if 37 or fewer points are scored in the game (10-0, 34-3, 20-10, 17-6, etc.), and it’s a tie and everyone gets their money back if exactly 38 points are scored (21-17, 31-7, etc.).

Or if the total for a baseball game is 9.5, the Over bettors win if at least 10 runs are scored by the two teams combined, and the Under bettors win if no more than 9 runs are scored by the two teams combined.

Side bets with a pointspread are generally the most popular way to bet a game for sports like basketball and football, while moneylines remain the most popular for baseball and some other sports, including individual sports like tennis matches. Sides, moneylines, and totals account for the bulk of most sportsbooks’ business. Many, many bettors in fact never learn any other kind of betting, never make any other kind of bet. Some of them even look down their nose at any other such bets as frivolous or dangerous novelties, like seasoned poker players contemplating a game with a bunch of wild cards.

In fact, there are at least as many opportunities for a savvy bettor to gain an edge with some of the less conventional bet types as with traditional sides, moneylines, and totals.

But that is a discussion for another time.