Definition of string bet
A string bet in poker is an illegal bet. It is the act of placing a bet in several stages. Imagine a virtual line that you cross when you make your bets. If you want to bet 600, for example, you can't take a 100 chip, bet it, wait to see your opponent's face, add another 100 chip, and see how they react. When you bet, you must do it in one step. You take the chips you want to bet and move them to the other side of the line in one move.
Tips to avoid string bets
It is possible to be a little off and not pick the right denominations and not make the right bet. For example, you want to bet 200??? by betting 2 chips of 100???, but instead you bet 2 chips of 50??? for 100???. To protect yourself and to play transparently, always announce the bet you want to make. By saying "I'm betting 200???" out loud, the dealer will probably let you add your extra 100??? if you should happen to bet your two 50??? chips instead of two 100??? chips.