Letter (message)  A letter is a written message from one person
to another. Letters, especially a regular exchange between two
persons (sometimes called pen pals), represent a kind of humanly
communication and mutual friendship. The role of letters in
communication has changed significantly since the 19th century.
Historically, letters (in paper form) were the only reliable
means of communication between two persons in different
locations.  As communication technology has diversified, letters
have become less important as routine communication. The
development of the telegraph, telephone, fax and the Internet
have all had an impact on the writing and sending of letters. In
modern industrialized nations, the exchange of personal letters
has become less common, being replaced by technologies such as
the telephone and also e-mail. With the advent of the compact
cassette, tape letters became a novelty.  By analogy, the term
letter is sometimes used for e-mail messages with a formal
letter-like format. Historicall