Said their thank-yous and departed.
When someone does you a favor and you want to express your gratitude for what they have done, this is an example of a time when you would say thank you.
When you are grateful to someone for doing you a favor and you bake him a pie to show your appreciation, the pie is an example of a thank you.
Origin of thank-you
- Thank you is a shortened expression for I thank you; it is attested since c. 1400.