Frets are the metal partitions or dividers used on a rouletteRoulette is a popular casino table game originating from France. Players place bets on either a single number, various groupings of numbers, the colors red... More wheel to separate the numbered pockets. When the ball is spun around the rim of the wheel, it eventually loses momentum and falls onto the wheel, bouncing off the frets until it lands in one of the pockets.
Frets can also be referred to as dividers or pocket separators. Some seasoned gamblers might casually call them “bumps” or “ridges,” although these terms aren’t as standardized.