Another common name for roll-over is a play-through. In most cases, when a bookie offers a welcome bonus (say, 50% of your initial deposit) it usually comes with a multiplying roll-over (e.g. 5x roll-over). Let’s take a practical example:
Let's say that you open an account with a bookie that gives you a 100% deposit bonus with a 4x roll-over, and your initial deposit is $100. This means that you must wager a total of ([100+100]x4) = $800 before you can withdraw your bonus.