The phrase "thank you" is a polite expression used to show gratitude or appreciation towards someone for their help, kindness, or service. It acknowledges the effort someone has made and reflects a sense of respect and courtesy.
The expression "thank you" combines the word "thank," which comes from the Old English "þanc" meaning thought or gratitude, and "you," which is the second-person pronoun. The phrase has been used in various forms throughout history, evolving from simpler expressions of gratitude.