A bonus code is a tool that you can use when registering at a betting site to avail a welcome bonus offered by the site to new players who sign up. The welcome bonus can be in the form of a deposit bonus that is equal in amount to your first deposit, a no deposit bonus, or free bets. A no deposit bonus is an amount credited to your sportsbook account that is not linked in any way to the amount of your first deposit. A free bet allows you to place a bet without having to use your own money. Thus, a bonus code is a key that helps you to grab any promotional bonus offered by the betting site.