a formal, well-organized piece of writing and is serious in tone)

A letter written to someone to get information, or to talk about a problem.

A formal letter written to someone to give or get information, or to discuss a problem.

A business letter is a letter written in formal language, usually used when writing from one business organization to another, or for correspondence between such organizations and their customers, clients and other external parties. The overall style of letter will depend on the relationship between the parties concerned; however, there is a general consensus on style , for example, Business letters usually follow a left-blocked format, other points of general style are outlined below.