1. A happy or friendly expression on the face in which the ends of the mouth curve up slightly, often with the lips moving apart so that the teeth can be seen. 2. To have, produce, or exhibit a smile. 3. To look or regard with amusement or ridicule. 4. To bestow approval. 5. To appear pleasant, agreeable, and non-threatening. 6. Most smiles are fake. A genuine smile occurs when the corners of the mouth go up, the eyes narrow slightly creating crow’s feet, and the upper half of the cheeks rise. This is a direct result of feeling happy. Physiological changes include the heart beating faster, blood flow increasing and skin temperature rising.