A letter is a written message conveyed from one person to another through a medium. Something epistolary means that it is a form of letter writing. The term usually excludes written material intended
News from My Lad by James Campbell, 1828–1893 (Walker Art Gallery)
Letter of Darius the Great to Gadatas, circa 500 BC.
The Einstein letter from Edward Teller and Leó Szilárd to US President Franklin Roosevelt suggesting an atomic bomb project. Click here for page 2.
A thank-you letter from Katharine Hepburn to Alan Light thanking him for his condolences in regards of Cary Grant's death
An open letter is a letter that is intended to be read by a wide audience, or a letter intended for an individual, but that is nonetheless widely distributed intentionally.
Letter (message)
…be read in its original form by large numbers of people, such as newspapers and placards, although even these may include material in the form of an "open letter". The typical form of a letter for many centuries, and the archetypal concept even today, is a sheet (or several sheets) of paper that is sent to a…
J'Accuse…! is an influential open letter written by Émile Zola in 1898 over the Dreyfus Affair.
Bill Gates's Open Letter to Hobbyists from the Homebrew Computer Club Newsletter, January 1976