所谓温暖大概就是你笑起来
[suŏ wèi wēn nuăn dà gài jiù shì nĭ xiào qĭ lái]
The meaning of warmth, in this case, might be best described when one says you are the embodiment of warmth especially through your smile. So 'So-called warmth is probably your smiling face.' It illustrates the power of a cheerful expression bringing warmth and reassurance to others.