感恩戴德 is a four-character idiom (成语) that literally means 'to feel gratitude and esteem virtue,' but in practice it expresses profound thankfulness for a kindness or favor received. It is more formal and literary than 感谢 or 感激, often used in writing or solemn speech to emphasize the moral weight of the favor. The phrase functions as a verb phrase in a sentence, typically taking the structure '对某人感恩戴德' or used as a standalone response.