Of poor quality; low-grade or shoddy. Used prenominally to describe a noun ("poor-quality ~").
質の悪い服はすぐに色あせて穴が開いた。
Poor-quality clothes faded and developed holes quickly.
この店は質の悪い部品を使っているので、製品がすぐ壊れる。
This shop uses low-quality parts, so the products break quickly.
レビューで質の悪い商品だと書かれていたので買うのをやめた。
I didn't buy it because reviews said it was a poor-quality product.