beautiful smile; charming smile
A set phrase meaning a smile is so charming it is worth a thousand ryō (gold coins). Used to praise a lovely smile.
Everyone was captivated by her million-dollar smile.
That kid's smile is truly priceless.
笑顔 is a general word for 'smile' or 'smiling face', while 笑顔千両 is a set phrase emphasizing the high value or charm of a smile.
From 笑顔 (smile) + 千両 (a thousand ryō, an old gold currency unit), literally 'a smile worth a thousand ryō'. The exact origin is uncertain, but it is a traditional expression likening a charming smile to great wealth.