What is the ruling on wearing thin abayas, skirts, and fabrics that define what is above a woman's knees when she sits or walks?

The Shari'ah has not specified a particular type of clothing for women. Any garment that achieves modesty according to the Shari'ah requirements is considered a hijab. The purpose of hijab is to cover and prevent temptation. Therefore, it is not permissible for a woman to wear anything that reveals her skin or describes parts of her body.