A facial expression comprised by flexing the muscles of both ends of one's mouth, often showing the front teeth, without vocalisation, and in humans is a common involuntary or voluntary expression of happiness, pleasure, amusement or anxiety.
“He always puts a smile on my face.”
Favour; propitious regard.
“the smile of the gods”
verb
To have (a smile) on one's face.
“I don't know what he's smiling about.”
To look cheerful and joyous; to have an appearance suited to excite joy.