Traveling is the violation called when a player holding a live ball moves illegally with it, taking extra steps without dribbling.
Traveling is the rule that makes dribbling necessary. A player holding the ball may not run with it: once the dribble ends, the player gets a pivot foot and, under modern interpretation, a gather step plus two steps for a shot or pass. Move the pivot foot early, hop without releasing the ball, or take a third step on the drive, and the whistle blows, the basket is erased, and possession flips.
No rule is argued about more. The NBA's gather interpretation makes legal plays look impossible to fans raised on stricter youth rules, replay culture has turned borderline euro steps into slow motion debates, and FIBA applies its own closely related standard, so the same move can be legal in one competition and a violation in another.
Historically the rule shaped the sport's look. Its strict enforcement in the early game kept basketball a passing sport, and its gradual loosening enabled the explosive one foot finishes and step back shots of the modern era. Quizzes treat traveling as a definition to know cold: it is the violation every fan can name, argue about, and demonstrate in a driveway within ten seconds.
In use"The referee whistled traveling when the rookie shuffled his feet before the drive."