What does Leg Twist mean?
The inclination of right hand twills or left hand twills to “twist” in the direction of the weave. This creates jeans with pant legs that skew to the right or left, an effect easily noticed in the outer seams.
Heddels explains Leg Twist
Today, many manufacturers skew the denim before construction in order to prevent leg twist. A broken twill weave may also be used to avoid the issue.
On the other hand, some jeans are purposely encouraged to twist for the visual effect. In addition, raw denim jeans tend to twist over time with washing and wear as they have not been sanforized or washed. The matter of leg twist is very much a personal preference – some people feel more comfortable with straight seams, while others prefer the look of twisted seams.
Here is an example of denim with leg twist: