A biased roulette wheel is one that is off balanced and favors certain numbers over others. Theoretically every roulette wheel is biased in some way or another and some are more biased than others. This is just a matter of physics because no wheel can be absolutely perfect with ideal balance. Anything from wear and tear or microscopic weight differences can cause a wheel to go unbalanced. Even the small engineering flaws can cause it to not spin in a way that would give every spot on the wheel complete randomness.
For practical purposes, casinos have high quality roulette equipment that is as fair as possible. In the past though, casinos had old lower quality wheels that did not spin perfectly. Basically a wheel could be leaning over in one position and because of this, the ball spinning around would land on certain numbers more often than others. If someone was able to figure out what numbers these were, they could make a ton of money from the casino and this actually did happen at some point. In one case, a gambler actually broke the casino!
A biased wheel can be found by using computer software to find a pattern. Every time the ball is spun in the wheel, the number that it lands on gets recorded into the computer. After so many iterations, one can find what numbers the ball lands on more often. In fact, many companies that manufacture the roulette wheels need to use these computers to test out a wheel before it goes to the casino to ensure that there is a large margin of fairness and that there is no major bias in the numbers.
Cheaters can use the same technology to find patterns. It may not be useful to use this software on a brand new wheel, but it can be beneficial if one was to use this software on an old wheel that has seen a lot of use over many years. An old wheel is likely going to have some bias to it due to age and these are the ones that cheaters tend to go after. They can use the software to find the biased numbers and then bet on those numbers because their odds are better than the rest of the numbers. The computer can sometimes calculate the odds as well and depending on what variation of the roulette game you are playing, a lot of money can be won if those odds exceed the house edge or the odds that the casino normally has against everyone playing.
Note that a casino is a business and they need these odds in order to make a profit to stay in business. Every casino game has odds in favor of the casino unless you can find a vulnerability in the game. Dice control in craps is a way to beat the house in craps. Card counting is another method used to beat the house in blackjack. Finding a biased wheel is actually the way to beat the house in roulette.
Interestingly enough, you might find it obvious that you could not find a biased wheel by playing at an online casino but it is possible! You would have to find an online casino with live dealers with an actual roulette wheel otherwise the virtual software version of roulette uses a random number generator (RNG) to select numbers to perfect fairness. Live dealers usually have a real roulette wheel on a web camera where you could use your computer software to find the bias of the wheel over the internet. One of the deterrents is routinely switching out wheels with other random wheels, even at land-based casinos.
The drawback of using biased wheel software is it normally takes at least 5000 numbers to be inputted into the computer to find a pattern. If you have every played roulette in a casino, you know that sometimes you can only get 40 to 100 spins per hour so it would essentially takes days to find a pattern. More importantly, we are not recommending that anyone actually bring this software into a casino because it is illegal. You could risk getting thrown out of a casino and possibly serving jail time. This is just an interesting article for those who were interested.