Two Possible Definitions for Memoir
"A memoir is how one remembers one's own life, while an autobiography is history, requiring research, dates, facts double checked" - from Palimpsest by Gore Vidal (penguin, 1996)
"Unlike autobiography, which moves in a dutiful line from birth to fame, memoir narrows the lens, focusing on a time in the writer's life that was unusually vivid, such as childhood or adolescence, or that was framed by war or travel or public service or some other special circumstance"- p. 15 of Inventing the Truth: The Art and Craft of Memoir by William Zinsser (Mariner Books, 1998)
A memoir is a narrative, written from the perspective of the author, about an important part of their life. It’s often conflated with autobiography, but there are a few important differences. An autobiography is also written from the author’s perspective, but the narrative spans their entire life. Although it’s subjective, it primarily focuses on facts – the who-what-when-where-why-how of their life’s entire timeline. Booker T. Washington’s Up from Slavery is an example of autobiography – the story begins with his childhood as a slave, proceeds through his emancipation and education, and ends in his present life as an entrepreneur.
To define memoir, we loosen the constraints of an autobiography. Memoir authors choose a pivotal moment in their lives and try to recreate the event through storytelling. The author’s feelings and assumptions are central to the narrative. Memoirs still include all the facts of the event, but the author has more flexibility here because she is telling a story as she remembers it, not as others can prove or disprove it. (In fact, “memoir” comes from the French “mémoire” or “memory.”) In Night, the Nobel Prize-winning title, Elie Wiesel tells his own story about one period of his life – how he survived his teenage years at Auschwitz and Buchenwald.