What does minus 110 mean?

Reading it

American odds hang on the number 100. A minus price is what you risk to win $100, and a plus price is what you win when you risk $100. So at -110, $110 wins $100, $55 wins $50 and $11 wins $10. When you win you get your stake back with the winnings, which means a $110 bet at -110 returns $210.

Why it isn't even money

A point spread is built to make the two sides an even proposition, and if the book paid even money on an even proposition it would be working for free. No book I know of works for free. So both sides are priced at -110, and the difference is the vig.

The cost to you shows up in the break-even. At -110 you need to win 52.38 percent of the time to finish level: risk divided by total return, 110 divided by 210.

When the price moves off -110

You will see -105, -115, -120 on spreads and totals. That is the book adjusting the price instead of the number.

It happens most around the scores football games land on. A book holding a lot of money on a 3-point favorite may not want to move to 3.5, because games land on 3 more than any other margin, so it leaves the 3 where it is and charges -120 to lay it, and the spread on the screen looks exactly the same as it did an hour ago. The bet got more expensive.

Read both parts of the line. Minus 3 at -120 and minus 3 at -105 are not the same bet, and I'd never treat them as if they were.

I treat -110 as a convention, not a law. Books that deal -105 exist, and on a single game the price often differs from one book to the next. If I'm laying more than -110, I want to know why, and whether the half point or the side is worth it.

Most players look at the number and never at the price. The book is counting on that.