Take a dumbbell in each hand and lean over to left and right. What do you call the exercise?

I was doing this in the ofice's gym. The attendant (a staff with some instructor training, I guess) told me that that exercise is proven to be bad. I just want more opinion on this and recomended alternatives exercise.

Thanks.

Increase waist size? I thought it tone down the waist.

Thanks for identifying the exercise. I also wanted to your opinions if it was bad for you. The guy told me it is against the natural growth of the body and not recommended.