Are gym leggings squat-proof?

What does “squat-proof” mean for leggings? The term squat-proof leggings is vague and usually describes leggings that aren't sheer enough to see through.

When we exercise and stretch the material of our leggings in certain poses, such as squats, if the material isn't thick enough, it becomes see through. These are not squat proof leggings.

Many gym leggings are designed to be squat-proof, meaning they are not see-through or transparent when you bend or squat during workouts.