The no deposit bonus (also known as free chips) is type of cash bonus that doesn't require to make any deposit. The money will given as a gift to try to games in real money mode without using any credit card, bank transfer, paypal or other banking method.
The idea behind these offers is to give you a chance to try the games for real winnings. Most of these offers have limits on the maximum win that you can keep. It's made to avoid a situation when someone will hit the jackpot with free bonus.
There is no limit how many no deposit bonus promotions to use at all casinos. However, at only one brand is allowed to use only bonus of this type.