A commotion is a noisy disturbance. If you're trying to quietly concentrate on reading this, you wouldn't want the person next to you to cause a commotion, or it would distract you.
Commotion, which comes from the Middle French word commocion, means "violent motion, agitation." It can be a disorderly outburst or disruption, like someone yelling in the street at night, or five people arguing about someone talking on a cellphone while a play is being performed in front of them. Commotion can also describe out-of-control movement, like people pushing and shoving to get to the front row of a concert.