When things wobble, they teeter or rock unsteadily back and forth. A brand new bike rider is bound to wobble a little bit when she's pedaling down the street.
A cafe table might wobble annoyingly until you prop up one leg with folded paper. And, when you first step off an amusement park ride, your legs might wobble for a while. Your voice can wobble too, or tremble, especially when you're upset or nervous. People wobble figuratively too: "When politicians wobble on important issues, it's hard to trust them."