This is a situation where a casino gives you free money to play with in order to attract customers. The client is usually given a fixed amount free to play with before he makes his own money. The most popular offered cash bonuses ranges from 500 to 2500 USD within one hour to make as much money as you can within that one hour.
Once you are offered the cash bonus it is upon you to strategies on the gambles which you can easily win and make a reasonable amount of money. Most people wonder why the casinos offer these free cash bonuses to the new members and it is a big loose to the casino but due to the stiff competition they opt to give you a chance to play the games and to reduce your risks as the player.
They only do these knowing they are gambling with the fact that if you like their services you will definitely become a regular to their casino. They however have wagering requirements prior to cash out any winning to protect the casino from bonus abusers especially in the internet.