tax disc
noun [ C ] UK uk/ˈtæks ˌdɪsk/ us/ˈtæks ˌdɪsk/
圆形税讫证明（贴在机动车的挡风玻璃上，表示该车辆的路税已付）
in some countries, a small, round sign that you put in the corner of the front window of your car or other vehicle to show that you have paid the tax to use it