That's because they're part of a car's secondary or rear defroster; the lines are in fact super thin wires made out of metal and resin, either applied to the surface of the rear window glass using an adhesive or sandwiched between glass layers.

这是因为它们是汽车二次或后除霜器的一部分:这些线实际上是由金属和树脂制成的超薄电线，要么使用粘合剂涂在后窗玻璃表面，要么夹在玻璃层之间。