Bail is a promise to come back to court for your hearing. During what is called "arraignment," a number for bail will be set. This number typically gets higher for more serious crimes, because people facing more serious charges have more incentive to flee.

When you pay bail, you are promising to come back for your actual hearing, where you will be tried for the crime you're accused of committing. If you do show up for this hearing, you can get your bail money back, or it is paid towards your court fees.

If you do not pay bail, you will wait in jail for your actual hearing. This means you will stay in jail for weeks to months, without having yet been convicted of a crime. Unless a judge declares that you can be "released on your own recognizance," which means that you're using the honor system to promise to come back.

Many people are opposed to the bail system, because it affects the poor disproportionately.