Smile is a kind of facial expression, which is mainly formed by bending the muscles on both sides of the mouth. Some smiles include muscle contractions at the corners of the eyes, an action known as "Duchamp smile.". A smile without eye contraction may be considered insincere.

In human beings, smile is an expression of happiness, sociality, happiness, happiness or entertainment. It's different from a similar but often involuntary grimace of anxiety. Although cross-cultural studies show that smile is a means of communication around the world, there are great differences between different cultures. Some cultures use smile to convey confusion or embarrassment.