The very nature of the words should give you a clue. A welcome bonus is for new players and it is a welcome that not only encourages you to play at a particular casino but also helps your play along. It is free and extra money that you can receive. Many casinos link these welcome bonuses to specific games or terms and conditions which often include the amount of money you need to deposit in order for the casino to match it. These particular welcome bonuses which are the most popular are known as match up welcome bonuses, the casino will match any deposit you make with an equal match or percentage of what you are depositing.