An acknowledgement letter is a formal communication that confirms receipt of a document, request, or message. It serves to notify the sender that their submission or communication has been received and is being processed. The letter typically includes a brief summary of the received item, a statement of acknowledgment, and information on any further steps or expected actions. It's used in various contexts such as business transactions, job applications, or correspondence. The tone is professional and reassuring, ensuring the sender that their matter is being attended to.