A business letter is a formal written document that is typically used for professional communication between individuals or organizations. It is usually sent via traditional mail or email and may include various components such as a header, date, recipient's address, salutation, body, closing, and signature.

Business letters can be used for a variety of purposes, such as making requests, providing information, offering services or products, or conveying feedback. They are generally written in a professional and courteous tone and may follow specific formatting and language conventions depending on the type of letter and the industry or field in which it is being used.