Refers to a smiling facial expression. Often used in phrases like 笑顔を見せる (show a smile) or 笑顔で (with a smile).
Her smile is really lovely.
子供たちは笑顔で遊んでいる。
The children are playing with smiles on their faces.
She showed a smile for the first time in a while.
He greeted us with a smile.
Hearing the news, she broke into a smile.
Watching the child, a smile spread across my face before I knew it.
I was actually sad, but I put on a smile for the photo.
笑顔 is a smiling, happy face, the direct opposite of the sullen, displeased expression of 渋面.
笑顔 is a smiling face full of visible emotion, the direct opposite of the blank, unreadable face described by 無表情.