A memoir is most often a written record of events composed by a person having intimate knowledge of them and based on personal observation.  It can also be an essay or poem focused on a specific learned subject.   The word originated in France, where it is called a ‘mémoire’ , meaning memory or reminiscence. 

A literary memoir is a collection of memories that an individual writes about moments or events, both public or private, that took place in the subject’s life. The author provides confident and assertive statements of fact or belief. Although this  genre has historically been defined as a subcategory of biography or autobiography since the late 20th century, the genre is differentiated in form, presenting a narrowed focus. A biography or autobiography tells the story “of a life”, while a memoir often tells a story “from a life”, such as touchstone events and turning points from the author’s life. The author of a memoir may be referred to as a memoirist or a memorialist.